Actually, we do know. Witnesses report that Oisin Tymon did nothing to Clarkson, before, during or after the attack. It will be interesting to see the full facts, but as the Police are looking into it that probably won't happen for some time.
The BBC had no choice. They are held to even higher standards than most employers, due to the nature of their funding. I love Top Gear, and am sad to see it's end, but that does not condone these actions.
On a wider note, we live in a namby, pamby World these days, and I do think these sort of things could be handled differently. It's probably why he reported it himself, in an attempt to nullify some of the impact. Not all progress is necessarily for the better.