Yes, the iPhone supports double-tap to zoom, and it works reasonably well. I rarely have to pinch to zoom in or out in order to get a better view of the content.
Reminds me of the idea I've hear taught in programming: give users only one way to do something, and you dissappoint some people, but give them more than one way and you'll confuse everyone.
Indeed. I've seen people struggle with this in things like single vs. double-clicking, using scroll wheels vs. scroll bars, window edge-dragging, and keyboard shortcuts.