Our family owned a Mercedes 240D (71 peak horsepower at sea level) for many years. That car's performance was lackluster on a good day and trying to merge onto the Pennsylvania Turnpike (with very short acceleration lanes) was IMO quite unsafe. From that experience, I'm pretty sure that people are dipping into more acceleration than that car could ever muster.

I have no doubt that some people behave as you describe, but I think some of that is driven from a rational position of not wanting to buy a car that is incapable of anything more than their normal daily driving. If you need to accelerate quickly to merge safely into traffic, bringing only 75 [or 71] peak horsepower to the table isn't a comfortable position to be in.