Amazon sold almost all Kindle books for $9.99 until Apple, trying to leverage a share of e-book sales for its new iPad, goaded publishers into raising prices. They were afraid that text was being undervalued by Amazon, which wasn't making money at $10 but had quickly come to dominate the e-book market.
Ironically, Apple had driven a radical restructuring of recorded music prices by selling $10 albums for its iPod that had cost $15 or more on CD. Apple's interference with the analogous favor that Amazon did for readers was pretty hypocritical. It also didn't work. So far, the iBook store is a failure.