@Nick-Danger: it is or can still be in the player's interest, due to how well SteamWorks works for the game.
It's not in my best interest to play a game that is 'steam only' because:
-I don't want unnecessary third party software running in the background to play a single-player offline game
-I don't want steam collecting info on me, including unspecified personally identifiable info
-I don't need steam to find me MP partners
-I don't care for achievements, in fact I think they detract from games
-I don't need steamworks anti-cheats as I don't play with cheaters (just old friends)
-I don't need steam to make a game difficult or impossible to play via LAN or direct IP connection
-I don't need steam DRM to be constantly running (beyond a one-time authorization)
-I don't need steam monitoring my computer for game file fragmentation or out-of-date drivers and whatever else it does
-I don't want steam being the 800# gorilla with its market share
-I don't need to have my legally bought games rendered useless if steam bans me for innocuous reasons (like disputing mistaken charges)
Nothing steam provides can't be done, and hasn't been done, in other ways -- ways just as effective.
Steam is used not because it benefits players (as shown above) but because it benefits publishers and steam.
Some like steam and I'm glad they can get it. Some don't like steam and that some games give those folks no choice and force steam upon them, not good.
Actions speak louder than words. If publishers truly thought steam was a benefit to all players, and if players were truly what they cared most about, then it'd be optional not forced. The reason it isn't is because it benefits publishers to make it mandatory.