So really the capacitive screen drove the interactions. Input first, just like the mouse on Macintosh or the stylus on Newton, everything then flows from there.
On the web browser, I disagree with you (sorry!), the killer app of the iPhone was that Safari was the same Safari, with the same capacity and rendering, than on desktop.
It was completely new. Yes, you had to double tap on complex, non responsive websites, but every single (non-flash) site would render the same.
My 640x480 HTC Universal with a plastic keyboard felt antiquated compared to the 320x480 iPhone, especially starting with the 3GS