I agree @preparedwombat and I think that is something that many people overlook.
While the steem blockchain has no transaction fees, there is still a cost to operating on this network. The difference is the site is responsible for the "fees" instead of the individual users.
I also think the fact that they are going to pair each currency to STEEM means the internal exchange will be that much more valuable. After the hack last week, a decentralized internal exchange can only be viewed as a positive.