The stat people want to know is "Percentage of devices that shipped with iOS 3 that haven't upgraded to iOS 4". Grouping all the phones together doesn't answer

The stat people want to know is "Percentage of devices that shipped with iOS 3 that haven't upgraded to iOS 4". Grouping all the phones together doesn't answer that, since the iPhone 4 with iOS 4 will clearly be a big chunk that proves nothing about upgrade percentage.