I think it's kinda like a beautiful woman (or something to that effect) - it's the first appealing thing people notice, and if you're shallow enough it's the only thing you notice. It somewhat translates through to a casual (but not necessrily shallow) gamer - if it's pretty, it's good and you should buy it. Gameplay isn't considered nearly enough, but let's face it - as long as the only thing on the back of the box is pictures, graphics are gonna be the biggest selling point to most people. It's a shame, but that's the way it goes.