It's not just $150. Those tickets go on your record. If you incur several of them, in a lot of places at least, you can lose your license for a while. I don't think most people are willing to endure that.
And of course, if you're seriously loaded then you have some leeway. There was a quote in a Star Wars novel I read once that basically went, "Money is like deflector shields; if you have enough of either your problems go away."
So yeah, some things are going to affect people with a lower income than those in that nice Corvette you'll never own. But few people genuinely can't afford one legitimate speeding ticket, and even fewer are going to intentionally drive like an idiot if they know they need the $150 for something else.
In the end, I think that rules are rules. They must be applied universally, otherwise we just have double standards. Speeding isn't the worst thing in the world, but it should be punished because it can carry legitimate risks to oneself and others.