If today, wednesday 18th september 2013, we go on the Apple US page, we can see that we can preorder an iPhone 5c with home delivery for 20th september.
Every color, with every memory and carrier combination is still available. The possible combinations are 50, and only ten of them are delayed by a week.
It’s possible that Apple has imported from China so many iPhone 5c (millions?) in all possible variants to avoid preorder problems? And some reports are saying that production is low due to some problems with camera modules.
If you remember what happened with the iPhone 5, the waiting list was long, people had to wait until december! The new iPhone 5c has been announced last week and it’s not sold out yet? Usually Apple sells millions of units in preorders. Maybe there are too many colors and people want to see which one looks better in their hands? Or maybe because if you pay just $100 more you can get the 5s that has a much better quality?
Update 2017: Imho it was a failure, otherwise they would have made the 6c, 7c, and so on