That's a good question, and I'd be interested to know how this is generally solved (it seems the ipad just doesn't du subpixel AA). I don't see a problem with subpixel anti-aliasing if it's with rotation in mind, i.e. different rendering depending on orientation.

In context of the original post, of course, there's not much the ipad can do since the subpixel AA is already encoded in the image.