With lots of 1st-party and 3rd-party titles available, Steam is a dope way for users to experience their favorite games. Since that time, Steam is now a platform for Mac and PC users. Deus Ex Human Revolution) or have the Mac version as a separate purchase (eg. Lot's of games that have a Mac version do not have the Mac version available on Steam (eg. In every case I've seen including L4D2, you buy the game, not a specific version of the game.
Franchises that many players around the world enjoyed on their gaming consoles were usually available only on PC, with Mac gamers left behind. For years now, one of the aspects where PC users always were ahead of those of us with Macs was gaming.