Probably we will never know exactly how many people purchased the Lost & Damned DLC for Grand Theft Auto IV, since it’s a digital download, but it appears that the numbers are very, very high. So high that Rockstar’s addon is the best ever released on Xbox 360, according to Microsoft.

Even more, Microsoft’s Aaron Greenberg considers that Rockstar’s expansion on GTA IV is so popular and successful, that it would’ve even sold more copies than Killzone 2 – a PlayStation 3 exclusive and full budget game.

Speaking with GameDaily, Greenberg said that the Lost & Damned was “”the most successful game addon content we’ve ever launched” and “If that content was sold at retail, it would be one of the best sellers across all platforms. It would have outsold Killzone 2″.

Of course, this is more of a stab at Sony than a real comparison or proof that the DLC had sold well (although there are no doubts that happened!) However, it makes us wonder: could’ve The Lost & Damned sell better than Killzone 2?