It isn't just getting a fast car to go faster than the speed limit, some people don't like how long it takes to get up to speed in a slower car. Here in California if you take forever to get up to speed you are likely going to get a lot of people cutting you off. Me personally since I know a lot of the traffic lights on my routes will change in a certain pattern I enjoy using the power in my RX-8 to get me to the next light just before it changes and seeing everyone else miss the light, and that's while staying within ~5mph of the speed limit (and pretty much everywhere cops won't pull you over for only going 5 over).
Also around here while there *is* a speed limit it is almost a suggestion rather than a guideline. The speed limit on all highways in San Diego is 65, but the flow of traffic is usually around 75-85, and I've gone by cops at 85+ without them budging. Pretty sure they're more concerned with the more dangerous people on the road (drunk drivers, people texting/talking on their cell while driving, etc) than some guy who is just going fast.
OT: Dodge Viper, there's just something about those curves that gets me.