But the i7 rocks and you said yourself high end desktop so why wouldn't apple release it. Makes no sense.
These perform the same. A Xeon 5550 is the same as the i7 920, just has one more QPI connection to connect to another processor. High end desktops are really aimed at gamers and enthusiasts. The Xeon W3520 is the same as the i7 920 too but with ECC support and will be aimed at UP (uni-processor) workstations and servers on the lower end. The Xeons are for DP (dual processor) workstation and servers like the Mac Pro and Xserve.
Intel like to be as confusing as possible