I found this post from Dave Perry which I think sums up why the developer feel slighted by Game Stop. I sympathise with them. If Perry is right they'll begin pushing things like Steam and sharing profits directly with MS and Sony for downloads. I prefer hard copies though.
http://www.dperry.com/archives/news/dp_blog/used_game_night/
It's a short post so I won't excerpt.
1. As I said. I feel Gamestop should make a better offer for poplular used games that they resell, or sell them for less than they do. I have seen very popular games go for a measly $5 less. But, of course I can't do anything more than choose not to trade with them.
2. I feel a certain loyalty to developer that make games that I like. I want them to make as much of the money I spend as possible. The same as I want my favorite music artist to make as much money as possible and only want there lable to make what is absolutely necessary. The team creating the game is where everything of value comes from and if GameStop is, as Perry suggests, doing everything they can to keep used games being sold at a higher rate than new games while the developers "pay to put standees and posters everywhere" then I reason they are damaging the bottom line for the developers.
If I haven't been able to express my point of view adequately in this post then I need more practice writing and it is probably to subtle an issue to matter. Competition and technology will eventually sort things out.
Naturally, if you manage to sell your games for a better price, you are left with more money to spend. I don't see anything inherently interesting in that, just two stores with different margins and different kinds of services. Why is one considered bad and the other isn't?