STOP THAT STOP! 
OF, I think you're getting confused between webcams and digital still cameras perhaps?
What you say is perfectly correct for a digital still camera specs (aim for > 6 megapixels etc), but webcams are a different kettle of fish altogether!
For a start, most webcam windows are usually just 320x240, a 640x480 webcam is about the best amongst webcams you can get.
So when you say that the video would be terrible, jumpy and sound totally out of sync... this isn't right. Firstly it's the frame rate that determines how jumpy the video is - you should look for a webcam that will do 30 frames per second (fps) at 320x240 - most of them will do 15fps at 640x480 but if you can get one that will do 30fps at this resolution (which this model actually does) then that's a bonus, and will make the video smoother. (For reference, most webcam apps e.g. Messenger, that I've used only display the video at about 5 fps, 10 if you're lucky!)
So, IMO this webcam is a very good buy, and for £17.99 inc PnP, it should be very good value for money
