I was wondering the same, and seeing the comment page, I think this is caused by ostensibly promoting the game (including asking for a rating) in the comments (and also on the forum). Anyway, being a genuine reviewer is generally enough to get a fair share of votes. :)
Also, I noticed that having a navigator version may get you reviewers that are less serious about being fair to the game (since you get a certain amount of people that are just too frivolous to download a desktop game), so this is a double-edged sword: more votes, but they can be less fair.
(By the way, I am just about to test your game! ;) I use the Karma ordering, watching out for people really reviewing games rather than spamming. You are clearly legitimate. :))