As pointed out in the EULA by John Gruber, HD rentals can only be done on the Apple TV and are not transferable to a computer, iPod, etc.
ok fine, maybe they did this for licensing reasons, or maybe because an iPhone doesn’t want nor can play an HD version.
There is a solution.
Make the HD rental give the rentee a license to the SD version as well. If I need it, I can go to iTunes, download the SD version and put it on my phone.
The same key would be used, so if i was 12 hours into my rental, I’d only have 12 hours left.
Fair and works for everyone.