It's not about how you manage. As I work in the same profession, many businesses jumped on the iMac bandwagon as a solution to the void created by the Mac Pro price jump from PowerMac's. The issue that has come forward time and time again is that all-in-one systems are not convenient for a workplace.
I come from a workplace where most have something like a smartphone, tablet and/or a notebook. The amount of all-in-ones is huge. We do the same thing when something breaks as with the normal tower models: we try to get it fixed on the spot and if we are unable we'll move it to our lab. If this is going to be a convenience the user will get a temporary replacement so he or she can get on with whatever he/she does. This also provides us with more time to fiddle with the problem and get it resolved. Very handy when things get very complex. But most of all, users are more satisfied because a problem with their machine/device does not disrupt their schedule completely.
So yes, it definitely is in how you manage and not in what product you use. Whenever we order something new we have a surplus of say 2 to 3% specifically for temporary replacements. This way we buy ourselves time and make our users more satisfied. Simply put: if all-in-ones (or any other device) are an issue with maintenance/replacement you are doing it wrong.
How do we solve this issue when someone doesn't have a system to work on, and if the work they had been doing is on the system? Not all businesses use server's, and not all businesses have an extra system just lying around. If a part in a tower needs replacing, it's easy to replace and takes less time in doing so. It is not a "universal problem that applies to every company", not every company has the same setup. If they're using servers, great, much easier. However many design firms work off their all-on-one iMac.
You can swap the drive, you can create an image and restore it as well as many other things. What you are describing here poses more problems because there are many single point of failures that have been created. This puts the business at great risk. Or in other words: management is the problem here, not the product itself: only how you deal with the product.
If you've ever worked on an iMac, you would know just how arduous and time consuming it is to diagnose and repair. Notebooks are easier to repair (in general).
It highly depends on what the model is aimed at. Notebooks aimed at business use tend to be a little bit easier to open up but the fact remains that notebooks in general are a pita. They are about as hard as an iMac.
Couple this with limited user upgradeability (only RAM is upgradeable), the inability to offer an anti-glare option (even with a hood, iMac displays have been problematic for some, not all, businesses that require such for their work), many have moved to other platforms due to long term financial business strategies.
If you need to upgrade the device afterwards than you didn't do your homework properly before buying it or you are simply desperately trying to stretch a devices lifetime. Computers have a max lifetime. After a couple of years it is cheaper to replace them than to upgrade them since they are written off. The glossy panel is more of a personal thing (I for one strongly dislike them and think they should be banned for medical reasons (they are really bad for ones health because it is more fatiguing for your eyes)).
Btw, if you want upgradability you don't buy any other product but the Mac Pro. It is the only Mac that is actually upgradable. This is what I meant with doing your homework properly before buying something.
I have two clients in NYC who moved to either Mac Pro's or Windows built towers due to the fact that they cannot afford the down time should a component fail or they could not afford to upgrade to Mac Pro's from their G4/5's due to the huge difference in price.
What do they do when the psu fails? What do they do when the CPU burns because of a failing fan? What if 1 or more disk drives crash? Those are all components that will stop a computer from working at all causing the exact same downtime they were trying to avoid by switching from iMac to Mac Pro/something else. In other words, they haven't thought it through at all and simply moved to something else. Unfortunately it won't solve the problem(s) they are trying to solve.
Replacing parts on the spot is simple for IT, repairing an iMac is not and cannot be done on site (AppleCare is voided and it would take a long time to diagnose, take apart the system and assuming you have Apple proprietary parts, replace). As a former Genius bar employee, I know the specifics required with iMac's and it's not a simple procedure.
This is completely incorrect. iMacs can be replaced on the spot like any other machine. Only its components can not be replaced on the spot like many other devices such as notebooks. When it comes to machines like Mac Pro's one needs to have replacement parts on site. As a former Genius you are well aware that this is absolutely impossible for Apple products due to Apple's policy of user replaceable parts vs non-user replaceable parts. This causes simple items like hdd's/ssd's and memory to be on site but things like a processor try, cpu, etc. require the machine to be sent to an AAPR to be repaired. Most brands will have something like this. This is why lots of businesses simply replace the entire machine so the broken one can be RMA'd.
In the end, business management is realizing the best solution is moving back to systems that are manageable such as towers/mid-towers.
No, in the end business management is showing once more why they are not in the IT department: they fail at it. Moving back to something else is not the solution because the problems remain. Again, these are not iMac problems, these are generic problems for nearly any device on the market.
The components are swappable on site (Apple does not offer on-site services, unless a third party has a contract with Apple which is rare), and parts are easier to keep on site than an entire iMac.
Which confirms what I already said: components on site for Apple devices is simply absolutely impossible.
A business would be smart financially to think long term; would it be better buying 20-30 iMac's with limited service should one fail resulting in employee downtime, no coverage once AppleCare runs out in 3 years unless through a third party in which coverage plans may be limited or expensive, and limited display options for film editors/design houses?
Most businesses write off machines in 3 years. After 3 years they buy new stuff. Which is exactly why most contracts only last up to 3 years. If you spent a lot of money you can get 5 year contracts. The contracts for longer periods are for special machines like servers, mainframes.
Businesses that need dozens of systems saw a major price increase in upgrades, went for iMac's, and are now facing having to replace those systems.
Because that would be the time frame in which you write off computers.
If only Apple offered the form factor of a Mac Pro with i7's processors, I guarantee you they would see a impressive increase in business and high end consumer sales.
Businesses require different things which mostly comes down to management stuff (think SLA). What you are mentioning here is only for people who want a more affordable Mac Pro. I've never seen prices be a big problem with businesses because they know they'll make money with it. It is the consumer who is very picky with pricing, they are the ones that scream that Macs are overly expensive and they can get a Windows machine for half the price (they don't look at the quality which is halved as well).