I believe that selling a game through Steam is one of the best ways to advertise it. This is especially true in UO's case, where they have little or no advertising budget to speak of. If I were a new MMO player looking for a game to play, chances are very slim that I would be introduced to UO through the traditional UO Game Codes method of selling it. If it were available on Steam, that would potentially open UO up to a whole new audience who most likely would not have heard of it otherwise. That new audience may or may not actually purchase the game, but it couldn't hurt to try.