You know what else everyone else does? Run stoplights. Why? Because they think they can get away with it. And a lot of people do. There simply aren't enough cops to watch every light.
It's the same thing with deviantART. People get away with copyright violations all the time, because the admins can't check every single deviation submitted. But you know what? That doesn't make it right. A cop will give you a ticket if he sees you run the light, and the admins will pull your stuff if it's reported.
It doesn't matter whether you think it's right. You agree to abide by the rules when you sign up, whether you bother to read them or not. Whether you agree with them or not. I've drawn stuff that I won't upload to dA because it doesn't fit the rules. I don't blame dA for this, because I agreed to it in the first place.
Also, don't shoot the messenger! Sheesh. I've talked to other artists that have, in the past, politely noted someone with a copyright violation, along the lines of "You may not realize it, but you're not allowed to use [insert violation here] in your art on dA." Their reward for trying to be helpful and keep dA's artistic integrity up a notch is generally a nasty flame response.
So, in conclusion, if you have questions about whether or not your artwork is in line with the rules, read these faqs:
FAQ #157: Can I use things created by other people in my submissions?
FAQ #8: What are violations of the deviantART copyright policy?
Remember that by using dA, paid account or not, you are agreeing to their rules. Quit blaming the people who are helping dA keep the community to the standard it deserves.