Thinking about the price/speed tradeoffs, carrier brand images, and whether I'll be at home when this package arrives doesn't make my gut feel good. I still feel good that I've bought something, but shipping is a bit of a bad aftertaste. Prime dissolves that aftertaste and leaves a wonderful "I get to play with it in TWO days!"

It's just a focus on user experience. Companies solve genuine problems, and while people pay for solutions, they happily pay more for great shrink wrapping.