Why do you need "support" for a screen resolution? PC's have had different screen resolutions forever, why were there never news articles about "Firefox Gets Support For 1280x1024" or "Firefox Gets Support For 1920x1200"?
1920x1200 does not equal high dpi. Think 1920x1200 on a 10" display. If your app runs on a high DPI screen, and the OS and your app has no support for this, all fonts and UI elements become tiny, which is unacceptable.
Windows XP had abysmal support for high DPI which usually resulted in broken UI layout. Vista introduced "DPI virtualization" requiring you to declare and provide explicit support for variable dpi in your application. Otherwise it is run at 96 DPI and raster scaling is applied. This prevents any UI layout issues but results in a a blurry image. I guess Apple uses the same approach: if your app has no explicit support, it runs under raster scaling.
