From tech blogger John Gruber of Daring Fireball:

"The idea with Apple’s 70-30 revenue split is that developers and publishers can make it up in volume — that people aren’t just somewhat more willing to pay for content through iTunes than other online content stores, they are far more willing. The idea is that Apple has cracked a nut no one else1 has — they’ve created an ecosystem where hundreds of millions of people are willing to pay for digital content."

Unfortunately he’s missing a few complexities of the issue from the publishers’ perspective, most notably name-gathering (although many analysts are for good reason not sympathetic about its absence in Apple’s model), but it’s a good read and raises some important points.