I agree with @bag0 as well. The fact is, that although Button and Brawn were not the most competitive team in 2009 (the second half), they still extrapolated the results necessary to win the Championship, when others floundered.
Also, Barrichello didn’t have an ‘unknown strategy change’ in Spain. The team believed that a 3 stop would be quicker in the race, but Jenson and his engineer decided that given their pace, they would switch to a 2 stop to get some clean air, and it was that reason and that reason alone that JB won the race. His pace was better than Barrichello’s.
The second obvious mistake is that Button was no way at fault in the Spa incident. Grosjean was one hundred percent at fault for that particular collision, and I’m almost certain that Button would have gone on to score points in that race, even if it would have been just one or two. So, even if what you said about the rest of the season would have been correct, which is highly unlikely due to the amount of different possible outcomes when in different circumstances, Jenson would have either been level or one point ahead of Sebastian, meaning he would have won the title anyway.
My opinion still stands though, he may not have performed quite as well in the second half of the season, but he did what he needed to in the first half, which turned out to be enough. I don’t recall seeing any other driver achieving six wins that season, misfortunes or not.
EDIT: Isn’t it also interesting that there are no results changing to benefit Button? Only those that benefit his competitors that season. It’s not always the fastest driver that wins, but the one who was the best over a season, and the one who can maintain consistency. You can’t blame this on the car either, because the team need to build a car that is reliable as well as fast, otherwise Alonso may not have won in 2005, Raikkonen may have.