Doesn't Apple offer multi-user licenses for precisely this kind of situation? My understanding was that you can get 5 or more licenses for academic or enterprise use, and that these licenses often have a special upgrade discount for later releases.
Note that I actually haven't researched this. I just ran across a mention on apple.com.
Of course, it is common practice for larger install bases to hold back from upgrading to the latest/greatest. This is often a wise decision. The main point (in relation to the original article) is that you already have the majority of your machines at OS X.
Upgrade to 10.2 once the kinks have been worked out.