That is my point exactly. They released it because of a time schedule, not because it was ready for prime time.
A time schedule set by the industry and consumer expectations.
They either release something that disappoints a handful of people or WAIT to release and disappoint everyone.
Personally, I've been very happy with iOS 7, despite the bugs. I'm glad they released it when they did as opposed to waiting. I'd hate to still be on iOS 6 - even with iOS 7 in its current state. I MUCH prefer the UI and I use things like AirDrop, Control Center and shared photo streams (multiple persons able to add) daily.
The UI and features are worth a few months of bugs IMO. I get some people don't feel that way - but remember. The negative group is always the most vocal, but is usually the minority. There are countless millions of silently content iOS 7 users out there - my mother, wife, wife's mother and wife's grandmother included.
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Remember pre-iOS 7? The masses were contemplating lynch mobs if iOS didn't drastically change. Add to the fact JI took the reins from Scott F.
I think Apple under estimated the time required to iron out the drastic changes. In terms of Android, it's always been rock solid.
Don't know they underestimated as much as they had a specific timeline to get a lot done in and couldn't quite do it - so they got to a point where they felt like it would work for a majority of people and went with it.
Apple didn't set this annual release time frame. And at this point, consumers have come to expect it. See my post above.