Well, it ain't "sex sells", but rather "face sells".
I well remember the thing when the cover for homeworld 2 was changed by some marketing team to include the commander of the ship - Mrs. S'jet. To me, it looks ugly and I'd liked to have a cover with starships instead, but some marketing guys said that a face would attract more buyers - why they had changed it.
You can see it in different places, and "babes" are just another example for that.
People, faces, emotions, humanity.
"Body sells" ? <img src="/ubbthreads/images/graemlins/silly.gif" alt="" />
Actually everything mainsteam sells for a reason: it's mainstream!
Sex, violence, food industry...
Hey, I bet if Larian put a can of Coca Cola on the cover of Beyond Divinity, the game's sells would blow skyhigh <img src="/ubbthreads/images/graemlins/silly.gif" alt="" />.