OK, I get it, for the ultimate hardcore workstation user, the nMP is compromise. (This is also reflected in the pricing, as you could spec a cMP out for like $40,000 if you really wanted to).
For somebody like me, it's a great machine though. I write software, have many apps running at once, sometimes multiple VMs with server environments running, and I might have a game running to boot (sometimes I just stay logged into FFXI in a Windows VM).
My desk is cramped -- I literally don't have room for a giant box. I also find that I often have to move my computers around, something I always loathed to do with a tower.
Yes, it might be a terrible design for you, but that doesn't make it a terrible design for everyone, including myself.