I'm not too sure whether it should be down to Apple to support Windows Mobile devices via iSync, or if it should be MS's responsibility to make sure their devices work on Mac OS X. For a long time, Palm provided the iSync conduit that allowed Palm OS devices to sync seamlessly with OS X. It is only recently that this conduit was included in iSync by default (I think this happened when Tiger was released).
Should Apple be the one who provides support for Windows Mobile devices? Or should it be Microsoft/PDA manufacturers? /discuss
In any case, do check out
MissingSync and see if that works for you.