There’s one big way in which iOS 7’s release is different to the original App Store opening. Developers spent an entire year using iPhone OS before they were even allowed to write apps for it. Think about it: by the time they started typing square brackets, developers had become intimately familiar with iPhone OS just by having it in their pocket every day for a year. That’s a luxury not afforded to developers this time around — they’ve been challenged to come up ground-up reboots of their apps just three months after finding out about iOS 7. - Scott Jackson
Interesting take on the App Design refresh happening when iOS7 is released. Although I disagree on the last section. It's true that developers only had the chance to play with the iOS7 design during this summer, but they've been experiencing the iOS paradigm since the iPhone OS.
So in a way, the only thing that has changed is the way apps look, and it's a big change, don't get me wrong. But the underlying system hasn"t changed.