Rock, Paper, Shotgun has an interesting article (thanks Ryan) that examines the effect of essentially re-launching Unreal Tournament 3 in conjunction with the Titan Pack and the Steam sale and free-weekends.
Now, traditionally it's the case that when a multiplayer game stumbles, it doesn't get back up again. UT3 seemed destined to go gently into that good night, save for the occasional antagonistic comment about PC gaming from Cliffy "Cliffy B" B and Mark Rein. And yet, as we coast into the Spring of 2009, a game released in 2007 is suddenly the talk of town all over again. On the weekend before last, its players jumped by some 2000%...
...It's not Steam or Impulse specifically as much as it is game distributors finally realising how to leverage the internet, and that a game doesn't stop existing once its initial print run disappears from store shelves. Game retail and traditional advertising alike have never seemed such dinosaurs.