Actually users of free software are far less valuable to the success of the free software movement than *contributors* to free software. If you are a free software user on the iPhone platform, you are very unlikely to become a contributor, because the technical limitations prevent you from tinkering with your software that is most often required to make a contribution. Sure - you can report bugs, fix online docs and maybe translate the next version, but for majority of contributions the iPhone platform is rather useless.
If you already jailbroke your iPhone (enabling you to tinker), then you can install the software to it without AppStore.
In the end the benefit from having a GPL app be represented in Apple App Store is of miniscule benefit to the free software community. So much so, that I would argue that the benefit of this FSF action (to public awareness of free software) is actually greater than the benefits all GPL software in the AppStore has brough so far.
Other app stores on mobile devices do not suffer as much, because it is easier to install an non-approved applications onto Adroid, Maemo and even WinMo devices.