I watched the BBC F1 forum tonight as forgot to on sunday and replayed that one.
In my view Massa was set into a strange path of disaster when he jinked right to avoid petrov's erratic movment. He then didn't back out of the half commitment on the inside. Instead of clipping the car in front ala webber / hamilton last races he took to the grass and then in turn speared someone. Silly mistake. Bit of a thoughtless and desperate act of the moment. Not petrov's fault but a chain of abnormal events.
Thats my view anyway
From what I recall Massa's incident was a pretty complicate turn of events. He had one opportunity to allow Rosberg to take the line, but there was also another opportunity to brake into a position along side him and take the inside. His third choice was to take to the grass. But, prior to this, the setup was that Rosberg was positioning himself to take the turn. However, Rosberg found himself being squeezed to the inside by someone from the outside. So he started to drift to the inside. Then he noticed Massa coming up from the inside and jerked left again. Massa's opportunity to brake-in behind Rosberg was just a fraction of a second before this.
It's so important to be aware of your situation and judging the speeds and distances to cars in behind. From what I recall there had been room behind Massa to brake and slot in behind Rosberg. But, was there time for Massa to double check his mirror's to make sure? I don't know, but that move means taking your eyes off what's developing in front, so I think that's why Massa chose the grass instead of braking. Rosberg, seeing Massa's decision to take to the grass, recovered from his left twitch reaction to Massa and continued back into the turn.
I may be corrected, but I think that's how it played out. I only recall it being a race incident. I wish FOM would stop taking down clips from YouTube.