Aaaand I also got it wrong (and it's actually implied in the bit you quoted):

http://community.livejournal.com/lj_maintenance/128843.html?thread=12225611#t12225611

Comments/community posts only get deleted when the account has been suspended.

So even IF they were to delete users for being inactive even though they posted comments / community posts those wouldn't get deleted - because they've "only" been deleted, not suspended.