Stephen Windwalker's Seeking Alpha article clears up any questions I had about the 22% figure. When I followed Engadget's live blog of the event, the 22% certainly seemed to be of all ebook sales - although I assumed it must be for only the Agency five.
As others have said ~10% of the US market for a new ebook store is very good. This may already be comparable with the Sony Store's sales. Also, much of this is presumably from new ebook customers - since Amazon and B&N have iPad apps. So the iPad is likely accelerating ebook adoption.
|