True, Apple's stated reasons are even simpler and more sensible: you can't advertise compatibility to a pre-GM application or device. That's part of the rules, and explicitly stated in the original rejection message.
GM stands for Gold Master I believe. Apple's concern therefore isn't that the device isn't out yet, it's that it's not finalized, and they don't want an app update to say that it supports something which isn't finalized yet because it could change tomorrow (even if that's unlikely).