Just because a piece of code is licensed under GPL doesn’t mean that the copyright owner(s) can’t license the code under another license, aka the license to Apple. The issue comes when an entity is using GPL-ed code that they don’t also own the copyright to.
According to the iTunes page it is licensed under GPL [1]. So in this case apple would be violating the GPL by distributing it under their terms of service (which in turn would then probably be a violation by Savoir-faire Linux for uploading it). The question then is, who except for the copyright holder could really enforce the GPL.
By signing the Apple Developer agreement you grant certain rights to Apple with regard to submitted apps--this is in addition to any other licenses such as the GPL. Putting GPL in the app description does not override these rights and does not force Apple to follow the GPL to distribute your app. The issue is that if it is not your code, but someone else's GPL code, you have no right to grant Apple these rights above and beyond the GPL.
So my understanding is, if you are going to have a copyleft-licensed app, that accepts contributions from the community, you need to have a CLA that assigns all copyright to you (or specifically authorizes you to grant Apple these rights). "Vanilla" GPL code from someone else cannot be used in an iOS app.
Another possibility is you allow people to make their own derivative versions by licensing it under the GPL, but you personally do not accept any contributions from the community. In this case, you own all the copyright and can license it to Apple as needed.
Most GPL software is not wholly owned by a single entity. You can re-license your own code, but you cannot relicense all the GPL libraries that you linked into.
