The capacitive touch and the accelerometer allowed them to make a web browser that could display 'normal' web pages. Up until then everyone had been dicking around with mobile web sites and the lack of ubiquity and cost of doing so... as well as the often hamfisted attempts to assume why you were on the website from mobile... all of these hamstrung mobile browsing adoption.
With this in place commerce could begin on the phone. Once everyone added mobile pay options it could end there as well. An now everyone has one, if they can.
My mom had a touch-capable phone with a resistive touchscreen and hated it. Her fingernails were not huge or anything but they were long enough she had to press with the pad of her finger, not the tip, and it crippled her accuracy.
