It already is a monopolistic entity
How is it?
Let's look at
this piece of news. Retail was still ahead by 2m units, and right behind Steam is Direct2Drive. That was earlier this year, and I doubt it's changed by much.
With Impulse, Direct2Drive, GamersGate, Metaboli etc selling digital copies of games, Steam can
not be a monopolistic entity. It has competitors, and those competitors often carry games that Steam doesn't (And, in return, Steam carries games they don't). The vast majority of PC games do not require Steam (Nor utilise Steamworks as DRM), either.
