Q about Apple Cinema Displays 20" vs 23" HD

Factual Questions
1

I just bought the 20" Cinema Display. Love it. My question arises from a dispute between me and a friend of mine:

Apple lables the 23" as an HD monitor while the 20" is left in the cold. Is there some technical reason why a monitor with a resolution of 1680x1050 (20") can’t play video from an HD source? What’s the magic behind the 23" HD?

2

The highest HD resolution is 1080i, which is 1920x1080. The 23" Apple display is 1920x1200 so it can show the whole picture, while the 20" is a bit too small in both directions.