That pentaprism must be HUGE to allow for 100% coverage. It's a real professionals camera, I'd be willing to bet it would self destruct if it was paired with anything other than a luxury class lens. My question to Canon is this: If you are going to charge $5,000 for a DSLR, WHY is there not a full-frame sensor?!! Seems kind of silly to me to allocate that much light sensitivity to a small sensor...and in such a huge body.
Try reading some of the posts above, which do address some reasons why Canon go for APS-H sensors. They will be offering the 1Ds Mark IV at some point as well, which will give you FF sensor. Note, APS-H is 1.28x crop, not the 1.6x crop of APS-C seen in the 7D/50D etc
As for the size of the prism? It's identical to the one used in the 1D Mark III - there's been zero changes to the viewfinder.
Oh, and yes, it's a pro camera. Obviously. The 1 series always has been, and always will be. They have to be paired with good glass.