How do they get 3.6x optical zoom from a 2.7 - 5.2mm focal length lens?

A single 720p frame (1280x720) amounts to 921,600 pixels. Less than 1 MP - even a 1080p frame only accounts for just over 2 million pixels. Why do I need a 10 MP sensor to achieve this?

Even HD webcams from MS for instance boast 5MP sensors. Is it my maths or am I missing something?

If I am I'll get my coat now plus all the coats in the cloakroom of the school for the terminally dumbass'd that I obviously should be attending...

Re: why not 1080p. You're missing something :)

The sensor could capture 1080p indeed (which only requires 2MP), but compressing a 1080p video stream to MP4 takes a much larger amount of processing and bandwidth, which is harder to fit in a small digital camera (and drives the price up). A 1080p frame has more than twice the number of pixels that a 720p frame has...