The advantage of ActiveSync is "push" email notifications and integration of your Exchange calendar and address book with the base Android calendar and address book.
If you use IMAP to access the Exchange server, the Exchange server cannot wipe your phone.
If you connect to Google's servers (IMAP), Google cannot wipe your phone via their servers.
[1] On my Nexus One, the ActiveSync email plugin was pre-installed and I don't remember seeing the request for wipe permissions when I first configured it. When Google (or whoever) pushed an update for the ActiveSync plugin, it did ask me for wipe permission. That was my first clue that I sold my soul.
It is interesting that the Android plugin has some UI words about the authority to wipe the phone. In my recollection iOS did not display anything like that.
It is also interesting that Google's set-up tutorial for iOS promotes the ActiveSync method but doesn't mention remote wipe:
http://www.google.com/support/mobile/bin/answer.py?answer=13...
I've been going back and forth about having my phone linked to Google this way. I don't like the concept of handing them an invitation to remote wipe my phone. On the other hand, there does not seem to be a better way to do over the air contact syncing etc (without signing up for MobileMe). My current position is to also sync to my desktop as a "if Google dies somehow" data store and think of my phone as somewhat more disposable repository.