Bottom line is you didn't leave a safe stopping distance in front of you.
I'm sure everyone on this thread has at some point driven too close to a car on a motorway, but if in doing so we had caused an accident then maybe we would realise that it was our actions that had caused the accident, trying to argue "well everyone else drives too close" isn't going to cut a lot of ice with an insurance company.
Look at it from the other drivers point of view, he was driving along minding his own business and spots an obstruction on the road, he hits the brakes, checks his mirror and it's clear to the inside of him so he starts to move across to avoid the obstruction, in the mean time a person behind has not left enough room to deal with the situation safely so instead of being able to pull up behind they have swerved and started to come past on the inside thus performing an illegal undertaking manoeuvre and causing an accident while doing so.
You may not like it, but if you had left enough space to stop then the accident wouldn't have happened.