I'm starting to wonder whether the ACD line was ever really updated. It's starting to seem more likely that Apple just increased the published specifications to match certain competitors using the same panel.
For what it's worth, I decided not to play this game with Apple, so I bought two Dell widescreen displays using the same S-IPS panel as the 20" ACD. At least now I know exactly what I'm getting (not to mention two Dell displays for the price of one Apple display).