I was actually surprised to find out that most IMAP servers aren't push-enabled already. (Push IMAP has been in the official IMAP spec for at least a decade, and whenever I set up an IMAP server, I always enable push.)
Because of the iPhone, I hope both Apple and Google enable push IMAP. I've been hoping for IMAP from Google for a long time, and maybe this will finally get them to do so.