Another way to put this into perspective is that the STEEM blockchain is decentralized, and anyone in the world can make use of the data that is on it.
Consider the steemit site, like a "viewer" or "writer" to the block chain. There will be many competitors to steemit.com, which is by design. Some are starting to pop up already.
Your account itself, is usable both on steemit, or any other site that talks to the STEEM blockchain where the data is stored.
Just be careful when inputing your private keys and password on new competitor sites until you know they are legit. For now, steemit is the most trusted one.
Well said. I agree 100% :)