I dont think I'm being stupid really.
We have to remember that a lot of machines in corporate companies are leased from suppliers such as Dell and HP.
Most of these corporate leases are 3 years long.
Here is a list of companies I have or have had close links to:
3M - Windows Server 2003, XP Pro, IE6 (all new servers are 2K3 and will remain so until leases expire and 2K8 becomes the norm).
MS - Windows Server 2K3, Xp Pro, IE7 (again, leased as above).
HSBC - Windows Server 2000, 2003, XP Pro and IBM Mainframe, IE6 (not leased for branch but asset management is leased equipment).
Dell - Server 2K3, XP Pro, IE6 (not leased)
HP - Server 2K3, XP Pro, IE6 (not leased).
BMW - Server 2K3, Xp Pro, IE6 (leased).
Thats just a few of some of the largest organisations on this planet!
For all of these to suddenly decide Vista is King and make use of its technologies involves a lot more than just client roll outs. Servers need replacing (which cant be done until leases expire), then they have to be tested, not least for stability, but also for all 3rd party apps that these companies might run (OneBridge, Lotus Notes, Peoplesoft (to name a few)), cross platform pollination occurs which is a nightmare to support.
All I'm saying is that you will absolutely NOT find any of these companies proactively moving to Vista. Its just not going to happen. in short, it will easily be 2012 before some of these companies are fully Vistarised, only for MS to turn around and say, "hey guess what, lets start the process again!"