That's certainly not been my experience. While using Google like a Real Person, if I run into high-ranking results that are useless, I respond to Google's entreaty to fill out the "dissatisfied" form to help them improve.
Then, when the next major algorithm update comes out, I invariably find that most of the useless crud pages I reported are nowhere to be found -- along with just about everybody using the same form/technique for generating high-ranking crud pages.
So yeah, they can register another domain, but they sure can't do the same thing again. They gotta tinker and tinker and come up with something that beats the new algorithm. And then the whole cycle starts again.
The nice thing is, it's getting harder and harder to beat the algorithm. If 'twere not so, there would be absolutely nothing but spam in the top ten of every search result of any monetary value :-)