The OP wants to be able to view a movie bought on Google Play movies on a large screen TV, and was hoping that he could play it on TV by connecting the Nexus 7 to it.
To the OP: You can play any of your Google Play Movies directly on your computer. So if you wanted to watch it on a big screen, all you need to do is hook up your computer via HDMI to your TV, go to play.google.com/movies, select your movie, and click Play. You can then expand it to full screen. Not sure about HD content, though.
I think people often lose sight of the fact that the Nexus 7 is a sub-$200 device that already packs a huge punch, and was originally intended to be a budget-friendly device, not a do-everything ultramachine. If Google/Asus loaded more things in it like microHDMI out, SD support, and rear-facing cameras, we'd be looking at a device that is closer to $300, and therefore not as phenomenal of a value.