Four ... Brawns got over-hauled by more than 2 teams (RBR, McLaren, Toyota, BMW and possibly Raikkonen in the Ferrari and Force India at the fast circuits)...so you often found Button not in the Top 4 on the grid...It's hard, this year, to see Vettel qualifying as far down the grid as Button started to do.
I think that is at the crux of the matter with comparisons with 2009. (Not to mention that Jenson actually won the title!) There is not the same level of competition throughout the field as there was in 2009. Currently there is a clear top 6 cars. In 2009, towards mid-to-end of the season it was getting really competitive.
Thus neither Barrichello, Webber or Vettel were able to really prevail over the other two
and they were dropping points to others too. There were 13 drivers to stand on the podium in 2009 [Button, Vettel, Webber, Barrichello, Raikkonen, Hamilton, Trulli, Glock, Heidfeld, Massa, Fisichella, Alonso and Kubica] compared to 8 in (the more similar) 2010 [Webber, Alonso, Vettel, Hamilton, Button, Massa, Rosberg and Kubica].
Now, can anyone see Red Bull, Ferrari and McLaren falling behind
Mercedes, never mind the rest?