While this is true, in the end it will not be sufficient except you are the very first on the market maybe even at a new platform. But the past showed us that there will be always someone to pick up your game play ideas and remakes it with decent graphics and just earns more money in the end. This also shows that customers will chose the better looking option when there is a selection to make.

Popcap as a casual game producer is such an example. They just remake existing ideas. They made tons of match-3-games or a tower defense game (plants vs. zombies). They just do it better, with more units, better presentation, more particles, better sound, better music. And they port it to each possible platform. And it sells in the end. It works, they make tons of money.

This tells me, that game play is important, it is the base, the ingredient each game just needs to survive, but game play sells best with good presentation.