[escoz]

Apple could have told developers about this during WWDC, but didn't.

My guess is Apple decided to do this last minute, after they saw the number of iOS7-only apps that developers were submitting.

[prehkugler]

It probably would've been useful to know before iOS7 app submissions were open, but, if that's their reasoning, it's a chicken-egg problem.

[jimsilverman]

looks like they're fearing slow/low iOS7 adoption, considering how boldly they emphasize how few legacy iOS users are out there.

[melange]

No. It's looks like they are telling developers the state of affairs, so that they don't fear slow adoption.

[escoz]

Agree. Knowing that users of old devices will continue to be able to use your app makes me a lot more excited about releasing for iOS7 only.