It may have a state of the art physical design, but this is a design which has served virtually no function other than to make any meaningful upgrades impossible. If apple had at least kept up and offered systems with modern components then this could be overlooked to a degree, but they havent. Talking as a 3D user, the current top end mac pro is nothing short of laughable in terms of specs. A single CPU socket competing in a world of dual and quad chip workstations, Two immensely out of date GPUs which are exactly the same as the ones launched three years ago, in real-world performance they're beaten by a single low-mid range gaming card. The forums I visit are filled with post after post of mac users asking the windows guys for help picking a machine.
You simply cannot leave the same old machine on sale for 3 years and expect to maintain a market. At least in the past when apple did this it wasn't too bad because the larger cheesegrater towers were somewhat expandable and could be kept somewhat up to date, but the trashcans have no decent cpu options short of what they shipped with and most people would have maxed the memory out in the first place.
Put another way, if apple left it 3 or 4 years between iphones, they'd have people jumping ship; that's the current situation for pro macs right now