By "true 64 bit version" do you mean having all the APIs 64-bit? All of Cocoa and Carbon rearchitectured to support 64-bitness?
Do you seriously know how much work that would take, not to mention the inherent compatibility problems between two forked releases of the OS?
If you're comparing it to the different 32-bit / 64-bit Windows releases, you're not really getting it: Tiger supports 64-bit for unix type processes (which can of course be frontended by a 32-bit GUI), which will let you do anything you like with 64-bits on your Xserve, with no performance penalty.
If you were a super important Apple customer that has regular discussions with them over high level technical matters, you'd know it was a little more than a "Think Different" thing.
Go tidy your room.