I'm reasonably sure this is because in the US the rear brake lights are often also used as the turn signal and the hazard lights. Under hard braking on Europea

I'm reasonably sure this is because in the US the rear brake lights are often also used as the turn signal and the hazard lights. Under hard braking on European/Japanese cars the hazard lights will automatically come on. Because they're overloaded in the US it's hard to tell if it's that, or the brake lights flashing unless you're paying close attention to the middle brake light. Edit: Just seen the comment about the Pulse system - didn't know about that!