Looks like gamestop lost 269.8 million dollars last year which ended Feb 2, 2013. They're raking in the dough! Gamestop sells new games, and used games, so yes, dev's get their cut on new games. Dev's also build used games into their price, so yes, that initial cut covers the used games market. Gamestop is just a medium used in the aftermarket. Hey, does Ford get a cut if someone trades their car in to the dealer? Do they get a cut when the dealer sells it? What about used books? Where's the cut to the author and publisher? What makes game developers special?
You guys complain about a business that's providing a good service, hires employees, has to pay rent, utilities, etc, takes on risks... it's not guaranteed that the used games they buy will sell anyways. Seriously, stop complaining.