Although the Steem blockchain is decentralised, the Steemit website is unfortunately not. That means Steemit could be forced to not publish certain things that are in the blockchain. Another site could decide to publish all, but then they in turn will receive court orders or whatever. You end up with a game of whack-a-mole like the music industry is currently fighting against Bittorrent sites.
RE: Bye Bye Censorship: Is Facebook the New Myspace Now that Social Media is on the Blockchain!?