The easy way to explain it is to say that these televisions are not actually in fact 480Hz. What they are referring to is an artificial increase in the refresh rate to help provide smoother video. This is accomplished by tricking the eyes to see quick glimpses of images.

To get more technical:

Manufacturers have created a technology which inserts very short black frames between the original picture frames while the viewer is watching a video source.

The method utilizes the principle that the human eye does not “forget” light instantly. You know this from a very short flash that tends to stay on your eye cornea for a short time. By inserting very short black images between the other frames, you can constantly reset the human eye, in order to improve the perception of response time and refresh rate of a LCD-TV.

LED LCD HDTVs will grow as 2010 progresses, and it looks like manufacturers will be using 480Hz as a way to make them more attractive.

[Source: TVLampsnbulbs.com]