Retina and other Hi-DPI displays don't generally use the RGB column layout that ClearType and other subpixel rendering algorithms abuse to provide higher luminance resolution. Using ClearType on a PenTile or AMOLED display is just going to give you color fringing with no actual increase in resolution.
Indeed. On the other hand, all Mac displays and almost all external desktop displays provide the RGB pattern. Otherwise, there is still the option to disable the sub pixel antialiasing.
