When you're a great player you will play great in your weakest surface too. Federer is not a great claycourter, but he was constantly reaching Roland Garros finals because his level in the surface was good enough to beat everyone bar Nadal.
Roddick and Murray may be have a style that suits grass better but it wasn't enough for them to win Wimbledon.
Definitely. But even playing great he lost this year to Murray, DelPo and Roger. With that level on a different surface would be enough to bet them. it's gonna be really tough to reach 2011 level, thats the only way (to me) that Novak could win Wimbly again.