They've tested 1920 screens a number of times, including on the Macbook as of last December. Shhh, don't tell anyone I said that. I'm not surprised they introduced it at the current resolution, but I'd be very surprised if they don't release a higher resolution option sometime this year.

The API you're talking about is for resolution independent interfaces all around, it goes way beyond just changing a few default font sizes, so it's going to be a huge change. It's more involved than the DPI preference found in Windows - which didn't have a great track record IMO (I used to use it set to "Large Fonts" which is 120% or so and a lot of stuff would break with it).

The lack of user-based controls for these settings in Mac OS may very well be a reason for not having yet released the higher density display. But that doesn't mean Apple has been stuck at 72DPI. They've changed densities on a number of displays more than once before., including the 23" Cinema and pretty much all their notebooks.

Bruno