I remember 72DPI being the old Mac pre-OSX standard. But my 17" iMac G5 is 1440x900 pixels, and the screen measures 9" high.
So 900 pix/9" is 100 dpi - right?
BTW, I liked the fact that a 1" ruler in a draw program was REALLY 1" on the screen. Hopefully, 10.5 brings that resolution independent scaling technology I've heard of.