Included in yesterday's report by Apple to investors and analysts was a single stat that reinforces why iTunes still controls so much of the digital music market. Apple has nearly 800 million registered users. Impressively, users have grown 40% in just 10 months; and attached to every user is a credit card that enables one click purchase. That's a growth rate of 710,000 accounts per day, and on track to hit 1 billion users next year. Amazon, which does not release user stats, has an estimated that 82 million users monthly. But Apple has miscalculated. The company has been reluctant...

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