I'd have to answer yes to all questions if I were Steven Seagal.
I once drove past a 'fight in progress' on the sidewalk. One guy picked up a metal pipe and swung it like a baseball bat, connecting with the other person's head! The guy (who should've been killed) didn't miss a beat and kept on fighting.
If fighting/defence is the only reason for training, then buy a gun instead.
Hmm, where I live you _can't_ buy a gun (or carry one either). Any knives over a couple of inches long can get you into trouble also, so that's not really an option :-). In any case even in most places where you can buy and carry guns I think that it would be quite unusual for the average person to carry one around all the time.
Self-defense isn't the only reason that I train, but it's one of them, even in the age of guns.