I've never understood the justification for that logic. I can build a house cheaper than I can have one built for me.
But if we compare Apple to other manufacturers (because that's fair right?) how much is the machine you are talking about? Dell (Alienware) Area 51 gets kind of close 10 core i7, 512 Gb SSD + 4tb HDD, 32 Gb ram (configurable to 64 Gb), GTX 1080....no keyboard, no mouse, no monitor, no speakers.... 4,799.99
http://www.dell.com/en-us/shop/productdetails/alienware-area51-r2/dpcw04brhs
And it looks like something out of a nightmare to boot.
Definitely better off building your own rig than buying that or a Mac Pro.
While I'm comparing to Dell and you are talking out of date take a look at their all in one computers. Best model has an i7-4790s which is Haswell, 2tb 7200 HDD + 64gb mSATA SSD (not sure if that is some sort of Fusion but mSATA?), 1440p monitor (albeit touchscreen), GT 750M GPU for 2,699.99
http://www.dell.com/en-us/shop/productdetails/xps-27-2720-aio/fdcwlp1398s
The specs are literally and considerably worse than my near 3 year old iMac for a higher price than I paid nearly 3 years ago. You can find it for about the same price I paid for my iMac on Amazon....not exactly confidence inspiring when it comes to in store service and warranty.
It must be rough being Apple using PCIe SSDs, 5k displays, Skylake processors, relatively speaking high end mobile GPUs with their custom TCON, etc then be criticized for using old tech. Personally I think they do a fairly decent job as fast as tech moves.
I never said I would be buying an Alienware Dell. That would be like paying a lot of money for "bad" design.
The problem for me is that I'm stuck between two chairs. On one hand I care about design and as a home office I want my machine to fit into my house. Only Apple computers does that. If I would have bought a PC I would have bought it for the power only and I would have hid the machine as hard as possible.
But, because I'm doing a lot of stuff that requires a lot from the machine, I do notice the amount of cores in the CPU and the speed of the GPU. If I have 8 cores instead of 4, rendering time is doubled. and a GTX 1080 or AMD polaris would greatly improve the FPS in my 3d software viewports or when working in the Unreal Engine. With the iMac I get a overall great experience in everything around these things, but with a power PC I would get a lesser user experience in the general sense but working in these softwares which I use every day would be greatly improved.
Im not talking about building the machine myself, I would order the hardware I like, and a company would put the machine together and I would just click the power on button and everything is ready for me when I receive it.
When it comes to price that is not really the issue, the issue is lack of options from Apple. There is no way for me to get a really powerful Mac. Even the nMP isnt powerful, not in the right sense. You can get a lot of cores, but they have low ghz per core (so on softwares using less cores, like adobe applications the experience would be worse) and to be honest the nMP 3 years old, the prices apple have simply doesnt make any sense anymore.
If apple would offer an imac with AMD polaris 64 gb of ram (or 128) I would be happy for now - but they dont and you dont know if they will be doing so in the near future. I can gladly pay 8.000 usd for an iMac if I would get a FAST machine that also looks great and with OSX.
And, currently comparing hardware in a maxed out iMac its annoying to see what I can get if apple were on par with whats coming in the hardware market.
if I pay 4.500 for a ugly PC box, I can get
GTX 1080 (comparing that with the AMD M395X, you get more than double the GPU speeds)
128GB of DDR 4 ram 2400mhz (instead of 32gb of 1867mhz DDR3 - thats quite a difference!)
8 Core CPU 3.2GHz i7 (compared to quad core iMac)
the rest of course if fairly similar. 1tb of slightly faster SSD (but apple is delivering fast enough SSD) the screen I would get something like the 32" Samsung U32D97Q with 3840x2160. In this area it would be a downgrade, except for the size. (I would personally love though if Apple made a 32" iMac with desktop internals.)
All in all such a PC would not look great but it would be a powerhouse compared to the maxed out iMac. But as I said I love Apples hardware and design choices, but I hate that they are slow catching up. -and seemingly currently not caring about the Pro Market at all - and I need a powerful machine to work efficiently.
If, like you said, you dont see the logic in my reasoning, then I think you dont need or know the advantages of the hardware I need. Maybe the work you do have no impact with a couple extra cores or not the way it does for me?