If you dont do some of the "tricks" listed above, I am afraid its just chance to see if you do get a random move in. Personally, i am not a believer in clearing voids. I have had plenty of random move ins from people who swore they cleared their void. I think its always possible.
Hmm, that's news to me. Every time I've restarted and played without a campsite, I've never gotten a 10th villager...even with lots of traveling and Streetpassing.