Well, even if that weren't procedure, everyone knows a C172 can do a 180 degree turn without losing 700 feet without power. And it's MUCH smarter to land on a runway than on a river, road, into a building, etc. If there's a clear grass field a little further ahead, by all means, take that as your landing field, less chance of screwing anything up, but if there isn't anything open, turn around.