In the past, most PC games were released and tended to not require any special computer-based client to run. Since Steam's initial forced installation for Half-Life 2 things have changed. Now many companies release games that only work through Steam, and it looks like another big game is getting that caveat.
Bohemia Interactive have announced that ARMA 3 will be a Steam exclusive. The developer has seen a great deal of troubles recently, such as members of their team being arrested for a period of time due to alleged espionage. It has been a hard road for them but their goal is still to release ARMA 3 this year. As such, they feel the only way that will happen is with making the game Steam exclusive.
How does that work out? First, they want to make sure the game has one main version to download. ARMA 2 was notable for having various versions floating around that were not all necessarily the latest. Of course, using Steamworks for networking functionality is a benefit to both players and Bohemia. They won't have to draft up their own solution for multiplayer and instead let Steam do the work. There were a few other reasons discussed in Bohemia Interactive's blog for the shift to exclusivity.
Should more games be exclusive to Steam or does Steam need more competition?