Mr Optimistic - you have been paying attention. And is it for that reason, amongst others, that it is best to wait until the command to evacuate is given. You also make a fair point regarding taking action on your own initiative - this forms no part of any briefing that I know of. Another reason to sit tight would be to wait for the initial attack by the RFF to be completed. They have the ability to knock out small (brakes, small fuel leaks etc.) fires, most likely rendering an evacuation unnecessary.
I have also witnessed a few discussions about inappropriate people sitting in the rows by the emergency exits. They don't (and certainly will not) last long but it's a shame we have to have them. The best reason I've heard to date was proffered by a little old dear with a broken leg. That was "That restriction doesn't apply to me" she then went tell us that she had to have to extra room so she could keep her leg straight.