iOS 6 seems like a negligible upgrade to me in terms of features, which is one of the reasons why I'm still on iOS 5 on all my iDevices. (Of course, the Maps etc. etc. fiasco contributed to that, too.) I just can't imagine what might suddenly be so demanding in iOS 6, as opposed to iOS 5, that iPad 1 would be unable to handle it. After all, if there are next to no new features, what would justify the higher demand on hardware?
