It's a myth... I keep hearing this phrase over and over again but I have not seen any proof.
Sex sells, even in pixelized forms
How many of such games you bought? Or how many people you know bought it? How many parents bought these for their kids for Christmast :D How many of these you see on Steam? Can you name any that "made it big" and became famous? Is Minecraft (or basicly any top game) about sex?