It can't be the developer's responsibility.
The issue here arises when someone distributes the App with DRM (Apple). They are at fault. Not the developer/publisher of the App.
The terms of the GPL had not been violated until the first person downloaded the App from the App Store.
I'm sorry but you are wrong. When you upload an app into apples App store, you take full responsibility for the app, and you agree to Apples terms and conditions for Apple to distribute the app for you.
VLC should have read all of the terms and conditions to see if their apps licensing conflicted with any of Apples rules. Apple can't change the entire app store because one developer failed to notice that the app he ported voilated GPL. Its not Apples responsibility to sift through tens of thousands of different licensing agreements for apps that were ported into their platform, its the developers responsibility to make sure their app complies.
There is tons of documentation on all of this stuff in the Apple developers portal.
VLC failed to read apples terms and conditions, submitted their app, then cried because it violated their GPL. VLCs fault, not Apples. VLC has no leg to stand on because in the end, they agreed to Apples terms and conditions before submitting the app.
EDIT: Here it is, from the iOS developer agreement: (FOSS is Free Open Source Software)
3.3.20 If Your Application includes any FOSS, You agree to comply with all applicable FOSS licensing terms. You also agree not to use any FOSS in the development of Your Application in such a way that would cause the non-FOSS portions of the Apple Software to be subject to any FOSS licensing terms or obligations.
The bottom line is, if anyone wants VLC, grab it now because Apple is going to yank it for sure.
EDIT2: I just realized I sound nasty in this post. I mean no offense Daveoc64

I'm just trying to weed out the details.