but the games are there for fun, and you cant just say 'you can only post once, and NEVER again'. Also, not everyone wants to play these games, so if you dont let the people who want to take part in the games, actually post there, then the thread will die pretty fast. Though i agree that seein the same 2 ppl over and over gets a bit annoying, i think there are other ways to solve that problem rather then just not allowing them to post anymore.
One thing that could be done is a courtesy system. If you've posted once, try not to post again until a few people have posted. And if no one except the same 2 people post anyhitng for like 7 days straight, then just let the topic die.