At the recent HD2 launch event HTC's CEO Peter Chou indicated a good point of view when comparing HD2 and iPhone. It is the screen resolution. The iPhone sports a relatively low screen resolution of 480 pixels down and 320 across, but the latest Windows Mobile device, like the HD2, has 800 pixels down and 480 across. In short this means that more data can fit on the screen at a time, translating to less scrolling in email, a higher resolution view of photos, better web experience, etc.

Here is the video from HTC HD2 launch event in Taiwan: