I have to say that *usually*, when something is GPL'd, I think the binaries should be provided for the same cost as the code itself. If you're selling a product, the code should only be available to the people who purchased it (at least, from you directly). I dislike people who take code that isn't theirs, compile it, and charge people for their "service". The whole X-Chat Win32 binary thing comes back to mind...

Now, I certainly know the license well enough to admit that it isn't required to give binaries for free, but I just feel better when binaries and code are equally free. Your situation, however, is very very different. I don't see you charging for your code: it's 100% free to EVERYBODY on your site. What I see you charging for, whether you admit it or not, is a SERVICE... the service of compiling the software for the iPhone platform (which by itself, I'd dismiss as something payment-worthy), and keeping it on the Apple app store (which costs you $99 a year). So unless the end user has a jailbroken iPhone, the code to them is really useless (if they just want to play the game). Thus, I think you're certainly more justified than you realize (not just legally, here) to charge a menial fee for your compiled objects.