That is probably the most rediculous thing I've heard all day. Care to share what sources you have for that statement?
Mr. Run N Gun sounds a bit more on target, although you can't simply look at what gun has killed "you" the most to determine the most used gun in the game. (it's probably the peacekeeper though...)
DSR passes the eye test for most used gun. There isn't a game that goes by where someone isn't sniping me from 5 feet away. And most used doesn't necessarily mean most kills. I would say most time equipped.