The thing is that to the rest of the organisation there are probably the following problems:
- they don't know what a wiki is, and they don't much care. Even though they use wikipedia they don't necessarily grasp the concept behind it: They just see a single entry, happily oblivious to how it got there.
- they don't want to learn what a wiki is, unless it directly helps them in the short term.
- They have ingrained ways of doing things. Changing people's behaviour is like changing direction of a supertanker: It takes a lot of time and effort.
The solution is to keep pushing it, paying attention to the following:
- Make it worth people's while in the short term. Reading your post it sounds like you may already be well on the way here.
- Make it easy. Usability should be top-notch, and there should be help available everywhere. If it's as simple as a mac it will be much easier to turn people around.
- Make sure that some things can only be done in the wiki, forcing people to do it. Don't put people's e-mails in the wiki, force them to do so themself.