Lafiel on 25 February 2013
Sony never restricted the use of K&M for games (Unreal Tournament 3 uses it for gameplay on PS3) , but devs didn't want to introduce these into their games, because K&M players in multiplayer FPS/TPS and RTS games have a big, big advantage over pad players and might therefore sour the experience for the majority.
And devs probably didn't want to spent time to balance single player for this input method either.
