FORTUNE -- When Apple (aapl) ran out of stock Friday and had to turn away thousands of would be iPhone 5S customers, a reader who calls himself iDawg tweeted a question that was on a lot of Apple watchers' minds:
Not as many people were asking that question Monday morning after Apple reported that it sold more than 9 million units of the iPhone 5S and 5C, 80% better than its iPhone 5 sales last year.
But we went ahead and put iDawg's question to Asymco's Horace Dediu anyway.
"It has nothing to do with operational genius," he wrote. "Every year they expand distribution and every year they fill the channel but initial demand grows faster than can be supplied.
"I will say one thing: Apple has a lot of information about demand which we don't. Having 400 million customers gives you a great deal of insight into markets. Certainly more than asking your friends."
Below: Dediu's chart of comparative launch performances.