When I think of monopolies, I think more of telecomms, of Wal-Mart and their selling at a lose to kill off competition, Microsoft purposely hindering the ability for competing software, and other examples. Unless I’m missing something, Steam didn’t do that, they were just first in the game and built a better product than the others did. Offering a better service that attracted customers. Now do I think it’s too large and would welcome competition, absolutely. But monopolies typically aren’t though just having larger market share with a better product.

If Steam did something like oh, pay developers/publishers to be exclusive to their platform, then yeah you’d have a good argument there.