I might argue that unless it's 1920x1080 at 1:1 full raster, it's not HD, and is rather "HDV."
Heh -- then you'd have to include all professional Sony HDCAM-based cameras (like the F900) and Panasonic DVCPRO-HD cameras (like the Varicam). Both of those codecs store a smaller raster to tape, and then expand to 1920x1080 on playback. (Of course, some of those cameras offer full 1920x1080 out via HD-SDI.)
Really, pixel dimensions are not an indicator of image quality, just as sample rate is not an indicator of sound quality. You can record at 96k, but if your mic and preamp suck, you won't have good audio...
A good measure of
resolution is lines per picture height (or sometimes line
pairs per picture height -- don't mix them up!). That number will take into account the whole system -- from lens to sensor to codec. If you compare the cameras on the market, you'll find that some 720p models outperform 1080 models. For example, the 720p JVC HD100 easily outperforms the "1080p" HVX200.
Of course, the larger the pixels, the more light-sensitive they are. Even the lowly HV20 technically beats the HVX200 in resolution, but the HVX is much more sensitive, so it will give you better images in low light.
Basically, it's a compromise between large pixels (high sensitivity), high resolution (measured in lines or line pairs), and low price -- pick any two.
I like the HV20 a lot, because it's very low price, fairly high resolution, and I can live with its sensitivity (I rate it at 125 ISO at 0db gain). If you need better sensitivity with comparable resolution, you'll have to triple or quadruple the price of the HV20.