nope, 4.0 was different due to Game Center. The whole point of GM coming out prior to public launch is a last phase of bug testing, thus why Game Center got pulled, as it obviously wasn't ready for public use.
Wow, you really don't understand how much integration it would actually involve! It's not as simple as that lol.
you're just not thinking logically here. Makes no sense to release GM prior to an event.
I don't think they ever intended on releasing Game Center with 4.0. Plus, it was announced when iOS 4 was originally announced and detailed at the April 2010 event and not when iOS 4 went into GM.
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I'm confused, how much integration does it actually require?