I see in the Top games with 10000+ votes and others with less than 1000. Is there a mechanism that reduces the game's score if it has a smaller number of voters (like imdb.com)?
Yes. Look at the BGG rating vs user rating on the games list here.
Keep in mind that 1000 votes is a lot for this site. As a result, the difference score adjustment between 1k and 10k votes is fairly small. Note that by sorting by num votes, just in the top 100 most rated games on the whole site, we go from 20k votes to 3k. Only 210ish games have 2k or more votes, less than 500 have 1000 votes.