Failing to avoid an avoidable accident is not the same as causing one.
Both drivers could have avoided making contact but in the end it was Vettel who actually initiated the collision.

There is little point in analysing something that happened in a matter of seconds as though both drivers had all the time in the world to consider their next move. This crash was more about the predetermined psychological mindset of the drivers than anything else. Vettel played the aggressor while Webber held his line and refused to be intimidated. Ultimately their egos collided well before their cars did.

The move itself will be debated for years (read the comments on Youtube videos of Senna and Prost's collisions — one driver has passed on and the other retired and yet people still argue over who was in the right). Vettel has done himself no favours and will now be on the back foot. Webber has an outright championship lead but may be doubting his position within the team. In the end we are the winners — it was a great race to watch and sets us up for some fireworks throughout the rest of the season.