Don't believe much of what you see in the movies. They play by movie rules, which have little, if anything, to do with real life. That said, when people are shooting at helicopters with high explosives and incendiary rounds, bad things can happen, and lots more than just the tail rotor can be damaged or blown completely away. There are lots of things on military helicopters that are far more flammable than seat cushions, including fuel and ammunition among others.