It's just common sense.

All the spiffy features on Vista is pretty much an old hat to me. I doubt they'll be able to fulfill everything they set out to do and meet the 2006 deadline. They dropped
WinFS for example. I'm guessing it'll be available on the decade anniversary of Windows 95 on August 24 or as late as December.
Compilation on everything that is known about Windows Vista can be read
http://en.wikipedia.org/wiki/Windows_Vista