Do CHP discriminate between cars they pull over?

The California Highway Patrol, or any type of traffic cops. Do they tend to only pull over cars that are luxury, sport and relatively nice? Or do they pull anyone who is breaking the law over? I'm just asking if they have a tendency to pull over certain cars over because I drive a relatively old car, I have sped from time to time like 15-20 miles over the speed limit...even in front of a cop car, but they never have pulled me over...except this one time for a busted brake light.