Nope, but if you've only been using the new ETK then I can understand why, it's quite a lot harder to ignite. Try the 1989 Pessima or one of the muscle cars, they catch fire a lot easier from front end damage typically.
I don't think so, they probably lowered the trigger bias or something. Ideally, fire should only occur when there is so much compression to fuel that it ignites, in other words, the most severe crashes (or because of bad design IE Ford Pinto tanks)
also the etk has a diesel engine, maybe that has different effects. depending on the setup. i cant say because i never really tested it out.
You probably broke the gas tank when sliding over that cliff which will cause an immediate fire in those circumstances.