The holes on the top of Lego minifig heads aren't just to stick bricks on, they're also designed to help prevent children from choking.
Why is there a whole in the head of the mini-figs now?
We added this hole on the top of the head just in case any kids got one of the heads stuck on their throat. That way they would be able to keep breathing.
(HT: Gizmodo and Paul Hsieh.)