Now I understand, it's not the code itself that has a price(hence the 'THIS IS FREE SOFTWARE' notice at the top of GPL). It's the entire "product" they charge for. Thanks for the reply!
Of course, today you're probably not going to have a lot of luck selling something that your potential customer can just download from elsewhere for free. So, in practice, you're going to have to provide other services/benefits that go into a commercial product.
But there's nothing in the GPL that prohibits you from just selling a bunch of bits subject to the requirements of the license and calling it a day.
The FSF started out selling copies of tapes with Emacs on them, and then later whole CD collections of free software, including a mixture of GPL and non-GPL code. They even had a service for a number of years where for $5000 they would compile up a whole ton of software for whatever platform you were using, and send it to your business with t-shirts and manuals for the software.