The problem with letting only people who own the game vote is that ratings will always be positive. If you don't like the game, you don't buy it, and thus you can't rate it. I wonder if it wouldn't be more viable to hve something similar to Facebook "Likes". You only gather a "score" from how many people appreciate your game, and you can't be dragged down. But the problem I see here is that it becomes even more obviously a popularity contest rather than based on merit. But who am I kidding, merit and reviews had nothing to do with each other for a few years now.