Just a sidenote. I happened to accidentally wipe my WM6.1 phone about a week ago, and I haven't plugged it in to my Vista machine yet. In my case, I've found there's no need.
I sync with Exchange - which gets everything over the carrier's network. I installed some 3rd-party software via .cab files on the micro-SD card, and some I downloaded from the device's internal browser. My device is fully functional where I want it to be, without running the desktop version of ActiveSync at all.
So, while I am certain *some* 3rd-party software can only be installed via desktop ActiveSync, and *some* information can only be synced via desktop ActiveSync, it seems more-and-more this is becoming unnecessary. I'd rather Microsoft focus on working with the carriers (and developers, developers, developers) to get the last remaining items able to sync over-the-air than to have them focus on backwards compatibility with XP. Then, you can run Linux, MacOS, or whatever tickles your fancy and still benefit from a rich sync.
Clearly, this requires Exchange to sync calendar, contacts, tasks, and notes -- but you can access several (I think up to 6) POP or IMAP mailboxes, as well.