Why?
Not all "pros" need xeon server class processors. But quite a lot need internal expandability that the Mac Pro [no longer] offers.
Why do you need INTERNAL expandability? What the hell is wrong with EXTERNAL expandability?
The old Mac Pro was limiting. I had to pay extra for those drive bays and the extra cooling required and everything else in that enormous casing (which also came with a footprint cost), but 4x3.5" SATA is just not the right combination for me. And I never use the optical drive so why do i have to pay for that?
This machine is being touted as the most expandable Mac ever, and that's exactly what it is. With Thunderbolt 2 you can connect ANYTHING to it, without having to take up unused space (ie. with the previous Mac Pro's footprint) on your floor or desk, and without having to pay for configurations you don't need. This is perfect for me.
I'll concede that including two really expensive GPUs that are not changeable might be a problem, if that is in fact the case, but we don't even know that yet.
You're all complaining about how this machine won't be upgradeable in 5 years or even 2 years, but your'e missing one really important point. Macs are the most upgradeable machines ever, because they HOLD their VALUE. Sell this one in 2 years for $1000 less than you paid for it and buy a new one. This is almost the ultimate in modularity.
This Mac Pro is the way of the future, just like the original iMac was when it introduced USB and removed floppy drives and all the legacy connectors (ADP etc). Just like all the new laptops that are removing optical drives and the other old legacy connectors (FW, etc).
If you don't want to have to upgrade all your old legacy hardware then DON'T UPGRADE YOUR MAC PRO. Keep using your old legacy Mac and your old legacy hardware for as long as it keeps running for you.
I for one see a very comfortable future with this new design into the next 5 to 10 years. External expansion is perfect, because, sure, I have to upgrade everything to TB now, but once I've done that, I'm set for another 5-10 years. (I'm basing that on how long FW lasted) I can replace my Mac Pro in a couple of years without having to replace all my external storage and other options, because I just swap out the core machine (the Mac Pro), and plug everything in (via thunderbolt) to the new Mac Pro I get at the time. Then repeat 2-3 years later, or whatever.
This is the way of the future. If you don't like the future then keep your old Mac Pro or iMac or Hackintosh and stop complaining.
This is the ultimate solution. What the hell is wrong with you people?