To your response in:
Paragraph 2 and 3: This: https://www.macrumors.com/2013/07/2...-high-end-haswell-processors-for-macbook-pro/
Although the article here applies to the rMBPs only, I don't doubt that they're doing the same to the desktop Macs.
Paragraph 4: You don't have to frequently maintain your Mac and it still doesn't fail you. A Windows PC requires much more maintenance than OS X does. I've built a rig myself and two out of the four RAM slots on the motherboard shorted out within half a year (Gigabyte GA-Z87X). So now only two of the RAM slots are usable.
Paragraph 5: It always makes sense to have the latest OS for security's sake. Even with an antivirus. I know I can buy Office 2013 once for around a hundred bucks, but Microsoft will NOT make subsequent versions of Office that can be purchased one-off for lifetime usage. You can see that with Adobe already. They will not make CS7 and will only support Creative Cloud. Microsoft is following suit.
How is it limiting? You're limited if you use different brands of devices, because they all won't sync together (spare me the crap on Google's cloud services. Besides whatever you store in Google's services is the most easily available to the NSA). Perhaps you prefer an unintegrated and seamless user experience.
That is called iris which intel probably designed at apple's urging. However, any OEM can use chips with HD 5000-5200, the chips are not special made for apple and any HD 5000 series chips are the same within their SKU.
One piece of personal experience does not mean anything.
Why would you need a newer version of Office? The old one does pretty much everything that a basic to medium user would need. Likewise the OS upgrade is optional. There is nothing wrong with saying that you yourself would buy a newer version of office or windows but its incorrect to say that it is required.
Overclocked the iMac with 680MX/780MX in windows scores 5700 on passmark which is a very accurate benchmark for game performance.
There are only 7 video cards that money can buy that are better than that, 5 of which are recent releases. 2 of them are $1000+ cards that you cannot buy on any off the shelf computer.
Simply put the iMac is one of the best and in my opinion the best all around gaming machine you can get.
Yet you can overclock the desktop GPUs too.... (And passmark performs ridiculously good on nvidia hardware opposed to AMD; it is not a good performance comparison, 3dmark is better though still problematic). OC for OC the 780m will be close to or outperformed by 660Ti, 670, 680, 760, 780, titan, 780 Ti, 7950 Boost, 7970, R280X, R290, R290X, 7990, 690.
760, 660Ti, 7950, 7970, R280X are all very affordable cards when compared to the cost of an imac.