I guess it's just that I don't understand why someone would pay $5000+ for this machine.
Well, it's the fastest Mac you can buy, by far, unless you need double precision GPGPU, in which case the trashcan mac surely beats this one. And it's got a great, high-rez screen, and fast I/O, and it's small and neat and stylish, and to top off it's a Mac, which appeals to some people.
Looking at the pics of iFixit's teardown of the thing, and what strikes me is how beautiful it is on the inside. Everything so neat and tidy and well designed and well fabricated. Even the PSU is beautifully put together, with build and soldering quality a mile and a half above what you find in any PC power supply (none of the messy jungle of cables snaking all over the place, daughter PCBs sticking up randomly and so on), as well as everything color-coordinated black to match the rest of the innards. Basically all components are either made with black plastic or covered in black laquer, black shrinkwrap or black tape. Hell, even the silicone putty used to secure components is black. Who else would go to such extremes but Apple?
If I had stupid amounts of money I would definitely want one of these. 10-core CPU and Vega 64, that'd be real nice. Alas, I don't! And with the full metal enclosure of an iMac, you couldn't see any internal LED bling decoration either...