I reckon Hamilton and Webber's performance depends far less on the car's characteristics than does Button or Vettel's. For that reason you never see Hamilton or Webber winning 6 out of 7 races, but for the same reason you never see them getting in a rut in the same way. Even amongst Hamilton's 2011 poor form there were a couple of podiums and a win, even in his Championship year he was making stupid errors in Canada, for example.