As Todt said, the other teams are making Ferrari and Schumi look better.
As stated previosly, Schumacher came in to the team in 1996 and built it up from practically ruins and being a mid-grid team. Now after years of work and bringing in the right people to work around him, the team has been pretty much perfected. Look where we are in the championship this year. Michael has won 10 of 11 races this season, Ferrari leads by more than double the points of the second placed constructor, Renault, and it seems Michael can work any strategy Ross wants him to run. Wow.
Plus, only michael can pull off what he did in Magny-Cours a couple of weekends ago(an arguable point, but really, who else would have been able to do that in that short of a time period?). Switching to a 4 stop strategy and creating a gap of over 20 seconds to allow for one extra pit stop and still come out with the lead over Alonso. That was probalby the most interesting race all season. Wow.
The car has been the class of the field all season. Only recently has the team been challenged by other teams, so really that shows me how much further ahead and above Ferrari are over the rest of the pitlane.
SO really i'd say a combination of both driver and car are really the driving force behind the championship winning team.