Look at the first minute of this (UK users only):
http://www.bbc.co.uk/sport/0/formula1/29100402In the first minute of the video
(i) Button overtakes Pérez in turn 1
(ii) Pérez in the slipstream of Button goes to the right on the exit of turn 3
(iii) Freeze the video at 31 seconds, it is clear that Button's front right tyre is ahead of Pérez's front left tyre in turn 4
(iv) Freeze the video at 32 seconds, it is clear that Pérez goes outside the track limits and Button stays inside the track limits in turn 5
(v) Pérez comes back onto the track ahead of Button, keeps him behind for all it's worth
Pérez got ahead of Button in this moment because he missed the turn and used the runoff, that is the change in position was illegal.
So Pérez was required to forfeit the place or receive a punishment. No punishment was given, why?
I have seen the following arguments around the internet:
(1) Button missed the turn himself
(2) Button left no room for Pérez
(3) Button forced Pérez off track
You see in the video the Button did not go off track (iv) so the 1st argument is proved incorrect
Regarding the 2nd argument, it is clear that Pérez was never going to overtake Button in turn 5 because he was disadvantaged with worse track position in turn 4 (iii).
Button is under no obligation to go wide in turn 5 to let Pérez overtake.
Even if this argument is correct since when does that give Pérez the right to overtake using the runoff and keep the place? It doesn't.
Regarding the 3rd argument, it may be correct Pérez was forced off track looking at it but I am unconvinced that it was Button who forced him because Button was taking the normal line which he is entitled to do. Pérez really forced himself off in his desparate attempt to regain the place.
This incident should have been investigated and I believe a punishment should have been given to Pérez once it was clear he was not going to give up the place.
It could make a world of difference, just look at the constructors points:
5th McLaren-Mercedes 110 pts
6th Force India-Mercedes 109 pts