Several people have said that the App Store is wonderful for developers too because it will make it easier for people to find your apps, install them, you won't have to deal with bandwidth. However, I think 30% is simply too much. I design applications myself, and I work on apps for weeks. It feels wrong for Apple to basically say they are doing a third of the work. I think something along the lines of 5%, for bandwidth costs and the review process, would be more appropriate.
I think a lot of the amount is Apple being greedy, and I think people might rebel. I know I wont buy an app from the App Store when I can buy it from the developer's website and really reward them for their work. I don't think Apple deserves $3 of a $10 app. Devs might start imposing an "Apple tax" where the App Store version of their app is more expensive to compensate, or they just wont submit their apps at all. People might start putting a badge on their page that says "This app is NOT available in the App Store".
And Apple, what will this lead to? Fragmentation. You had a chance to give the world a really beautiful unified system, and I feel like you are trying to get too much out of it.