The wonderful black-hole that is iOS development, we (as in all Developers) were informed (not by Apple but by a tech blog) that users can install older versions of apps even AFTER you have released an update.
Yeah, me too... I was like WHAT???? Anyhow, just before I got kicked off the Apple Developer forums (seems I was a bit too vocal) several developers confirmed that yes Veronica there are Angels, er wait no.... When you select the checkbox entitled "Are you upgrading for a legal reason" (<- purposely using the OLD text, notice how they have magically updated the text so it is now only 30% unclear of what it means). This will prevent a user on an older, no longer supported version of iOS, say iOS 4.x from instaling on older version of your app.
Really this IS great news for users and crap-tastic for developers. One question immediately comes to mind, though:
1. If we DO NOT check that box (like I have NEVER, because I've never had to update FOR A LEGAL REASON!) but we DO REMOVE an older version in our Game Center compatibility, what does Apple do???
So there you have it, in all it's Apple-vagueness.