It probably helps sales, but I don't care either way. I'm not going to dismiss a game as sick filth just because it has illegally large tits in it, but it's not the chief selling point for me either.
I don't understand all this moral hoity-toityness about sex as a marketing tool though. I mean, it's always been used! Why do you think there are no unattractive people in ads? Ask yourself this, if you wanted to buy an item, and there were two market stalls selling it at the same price, both right next to each other with one being staffed by an attractive woman (or man, I'm just speaking from a male perspective here) and the other staffed by an unattractive person, which one would you buy from. Of course, the majority of people would say they don't care, but deep down they would buy from the attractive woman 99 times out of 100. Why? Because as animals, we are attracted to other animals of the same species, and it just happens, and it's the reason why sex is the most effective marketing tool there is. The whole point of marketing is to appeal to as many people as possible, and fewer things are more universal than sex. It's not disgusting, it's not degrading, it's just showing us what the majority of people want to see, even if they don't openly admit it themselves.