FWIW, on Windows WPF, Silverlight, and I think Direct2D were designed from the ground up to be resolution independent, with everything vector-based and all dime

FWIW, on Windows WPF, Silverlight, and I think Direct2D were designed from the ground up to be resolution independent, with everything vector-based and all dimensions expressed in "virtual pixels", but a lot of programs still use GDI, which is pixel-based. So it looks like the situation is roughly the same on Windows and OSX: new APIs are resolution independent, but until their use becomes more widespread people won't benefit much.