Different rules different tyres. Vettel could have actually went much faster than he had to to win these races. And not only that, I see where you are coming from with the speed of the car, but reliability of Vettel's RB7 has been Rock solid, (just a temporary KERS glitch here or there) and that makes a damn fine car to me.
Pole every race, fast enough to win on strategy... (I think China was just a cock-up, Vettel should have won.) Canada was a cock-up too.. Silverstone and Hungary... Vettel come's to every race knowing that he has the car and the backing to win COMFORTABLY. Can't say that for the other guys (Even Webber! lol).
So yeah, RB7 is waaaay better than RB6 in my eyes. I mean, It's the best car at Monza too! nuff said.