Bjarni once suggested that 8bpp works for him on 10.5, so apparantly not all 10.5+ does not handle 8bpp graphics. Nevertheless, it seemed that for some systems the already existing 'does this support 8bpp' did not work, i.e. the OS API seemed to suggest that 8bpp worked when it actually did not. So, I don't know what is going on precisely here but it's definitely not nice to suggest that it supports 8bpp when it doesn't. So just ditch 8bpp support for anything that we suspect might not support 8bpp...