It's apparently faster for an LCD panel to change from black to white (0-255) than it is to change from one shade of gray to another, so when response time is listed a lot of manufacturers list the black to white to boost #s, even though in the real world most transitions are grey to grey.

Slower grey-to-grey makes for choppiness in fast moving scenes, I think on my TV it's 6 ms and I still see it. 3ms is pretty good for grey to grey.