You want a real monopoly? Call me when you can't log into gamersgate, the humble store, origin, GoG or Greenmangaming and Steam is your only option. You wouldn't know a real monopoly if Time Warner came to your house, pulled out all your cables and forced you to sign their contract.
Monopolies don't just affect other businesses. They prevent the very existence of competition. You have choices if you know the google-fu.
Exactly. And you can even sell your game outside of Steam and still use Steam as the content distributor/updater for free. Valve only takes their 30% cut if you sell your game on the Steam store page.