Many online communities, and even big networks like Machinima are affected by this decision.
Youtubers make movies and shows using game footage, and I don't think the game creators usually mind. It all brings exposure to their games and companies.
And there are literally millions of indie and upcoming singers on Youtube creating cover songs, using beats/instrumentals that might be copyrighted.
Youtube has recently set it up so that these videos have a link to the original musicians channels, and sometimes a purchasable iTunes or Amazon download, so I don't think the owners of the original tunes complained much either.
Videobloggers are urged to oppose this bill! Write your congressmen, or Watch this video/Demand Progress to help.