I went a tech conference at local university, and one of the topics was Windows 7 migration. In fact, that university itself was a microsoft case study for that migration. Attach is link Microsoft Case Study: Windows 7 Enterprise - Villanova University
I'll post the most important facts I learned from the Villanova's presentation later. Hope this helps
We deal with lots of schools in our local area and have been doing Windows 7 deployments since last summer. We have encountered few issues as most software developers we have spoken to have updated versions of products which we have obtained for free. This includes 64bit windows as 50% of our deployments have been at this level. If you speak to most software companies they are pretty good as they would rather give you a free/cheap upgrade than lose you completely (and various other schools as the deployments increase).
I've just been having this conversation with the IT coordinator at one of my schools. She seems to agree, so hopefully the school will start asking for Win 7 machines which will force the need to enable the server infrastructure to cope with it.
You are right, I think that much of the pickup of other products like MacOS is because it is not competing with a modern equvilent but rather the 8 year old XP as people are unwilling to upgrade. All these revoloutionary features that people quote as reasons to switch exist in he modern equvilents of what they are actually using now but they just have not got around to upgrading it.
The newer OS is more reliable and cuts support costs, even if there is a reinvestment nessisary for some legacy tripe on balance it will probably be much better in the long run to move towards an upgrade.