I'm just wondering what Letterman precisely said about the Volt. Well, the next week GM had Lutz visit Letterman with the Volt. Lutz defended the Volt and explained to him why they couldn't release an electric vehicle earlier like Tesla motors. He also goes on and talks about why GM cancelled the EV1 car program. If you're not familiar with the EV1, it was the first purpose-built electric car produced by General Motors (GM) in the United States. If you haven't seen "Who killed the Electric Car" yet, I really suggest watching it. One of the main scenes in the movie was about the EV1.
If anyone gets a hold of the video of Elon Musk from Tesla on the Letterman Show please post it in the forum.