Saw it, loved it, hadn't even heard of the book until I saw it, now I'm interested and will probably read it.

SPOILER!!:
Really the rule change was as much a disadvantage as it was an advantage, being told that there is one alliance who you won't be able to wait out until one betrays the other to get rid of tells anyone left in the game that they need to focus on those two. So I mean plot wise yeah, it was totally so they could have a happy ending... at least as happy as a 24 man death match can end. But strategically speaking, that rule could hurt just as much as it helps. But then really, it doesn't seem like they really cared about making it a fair game, spawning random forest fires next to people and all the other crap they did to favor some but hurt others.