The GPL requires that the program include an offer to provide the source code, either on a physical medium or on a server. It does NOT require that it be distributed via the same server or service that binary is on. v3 makes that very clear, saying:
"the Corresponding Source may be on a different server (operated by you or a third party)"
Putting the binary on the App store and the source on Github is exactly what that covers - provided that in or "next to" the binary copy you make it clear where the source can be found.
Therefore, if you are distributing a binary via the app store, and distributing the source via FTP or Github, you're fine. v3 also says that you CAN distribute the source the same way that you distribute the binary, or you can distribute it using a different method. Also under either version of the GPL you can offer it on physical media.
So no, the GPL doesn't require that if the binary is delivered by mail (or app store) that the source be delivered the same way. In fact, it explicitly says the opposite.
The issue that FSF pointed out in another, more specific post, is that while Apple may not be required to do anything at all in order to conform with the GPL, they are in fact doing something. They are stating that all software distributed via the app store has certain restrictions. A more precisely fitting analogy, therefore, is post office policies about what can and cannot be shipped.
The FSF position is that the policy is an additional condition imposed by Apple which means that APPLE can't legally distribute GPL code under those conditions. That, however, takes us right back around to the question we started with. _I_ may distribute the software, as long as _I_ don't impose additional conditions. If I'm the one doing the distribution, it's legal. Apple is imposing additional conditions, but it's fine for Apple to have conditions on it's app store if they aren't the ones distributing the software. Just like the USPS has policies and conditions, which don't affect the fact that I can distribute GPL software by using USPS to do it.
Whether the person who put the app on the app store is distributing via the app store or if Apple is the one doing the distribution is murky. Viewing that phrase in isolation, a court could rule either way. However, the court will read the whole document, not just one phrase. The top of the GPL license says:
"Our General Public Licenses are designed to make sure
Okay, so the purpose is to make sure you can get source code if you want it. That's the goal of the license agreement. Given the murky question of who is the distributor, a court should look at the purpose of the document. The purpose is to make sure people who want source code can get it. If it's freely available on Github and the app contains a link to that Github, the purpose is being fulfilled and the court should allow it.