HD is more than just high resolution and huge TV screens--it's also better color. In this case, XvYCC color, a space that's able to encode a larger variety of colors that predecessors such as sRGB or YCC. Sony is first out of the gate to support XvYCC with its 2007 prosumer models, the HDR-HC5/7 and HDR-UX5/7, hard drive and DVD-based AVCHD models, respectively.
Of course, Sony being Sony, the company has branded its own version of the space as "x.v.Color". (Why the names always include random periods--think "i.Link"--escapes me.)
These models use 2- and 3-megapixel versions of Sony's ClearVid CMOS--it'll be interesting to see if it's up to the task of a broader color range--and now have an automatic slow-shutter mode for when the light starts dimming. The specs do claim a we-hope-its-true minimum illumination of 2 lux.
The HDR-HC7 and HDR-HC5 will ship in February for about $1,400 and $1,200, respectively. The HDR-UX7 and HDR-UX5 follow in March for about $1,300 and $1,100, respectively.