Own as in? Copyright? Or like Facebook where they technically own it all.
I cant answer definitive but I think copyright - no, of course, you would have to file that, however it is a great way to unoficcialy claim it as the blockchain is basically untamperable..
Second scenario, I dont think so and I have never seen anything in the terms of service that refers to steemit.com owning ANYTHING on the steem BLOCKCHAIN - the blockchain is sort of an unleashed beast - its not like a server that facebook has the keys to... good question though I will research it more...