I first heard about this in the context of the n900, which doesn't implement the remote-wipe functionality. And the n900 tells the server that it doesn't (it's not "provsionable", in exchange speak). And some exchange admins only allow provisionable phones to access the server.
Some users in the big talk.maemo.org thread about this asked for the ability to tell the server that the phone is provisionable even though it isn't. But apparently, doing that violates the license under which nokia got the exchange syncing code from microsoft.
If the people implementing the client software used a non-microsoft activesync implementation, then presumably they could give users some more control. I thought such implementations existed, but if they do then I don't see why people aren't using them.
Aside: what a horrid bit of functionality to hide under the anodyne word "provisionable". Doubleplus ungood use of language there.