People have posted links to the original thread and the FSF's long analysis, but a short summary might be possible. I shall attempt one.
One of GPL's requirements is that when you distribute GPLed code, you can not impose any additional terms on the recipient.
When a user obtains an app from the App Store, Apple makes a copy of the app and that is downloaded to the user. This means that Apple needs permission of the copyright owner to do this. For most apps, there is no problem, because the developer owns the copyright, and grants Apple permission to make and distribute copies.
When the developer has included GPL code that he does not own, and whose owner has not granted an exception for Apple, Apple has to obey GPL. That means imposing no terms beyond GPL on the recipient.
Unfortunately, Apple does impose terms on the user--you aren't allowed to use the App Store unless you agree to Apple's terms, which include limits on what you can do with the downloaded software.
It would take all people who own copyrights of code in VLC. That would include the VLC authors, but might also include authors of other GPL code that the VLC authors used.
If a GPL project hasn't planned from the start to allow for the possibility of granting license exemptions, it is fairly easy to let outside GPL code get into the project without its authorship being carefully tracked and documented.
One of GPL's requirements is that when you distribute GPLed code, you can not impose any additional terms on the recipient.
When a user obtains an app from the App Store, Apple makes a copy of the app and that is downloaded to the user. This means that Apple needs permission of the copyright owner to do this. For most apps, there is no problem, because the developer owns the copyright, and grants Apple permission to make and distribute copies.
When the developer has included GPL code that he does not own, and whose owner has not granted an exception for Apple, Apple has to obey GPL. That means imposing no terms beyond GPL on the recipient.
Unfortunately, Apple does impose terms on the user--you aren't allowed to use the App Store unless you agree to Apple's terms, which include limits on what you can do with the downloaded software.