Obviously the Tesla Roadster is not competition for the Volt- one is a niche sports car, the other is not. The Roadster is very good at what it does, knocking the socks off many gasoline powered sports cars that cost twice as much. The thing GM needs to be on the defensive about is the sedan.
The Tesla Roadster claims to get ~220 miles on a single charge. That's with sick acceleration and I'm sure a transmission geared with that in mind. I know the Volts range will potentially be a few times this number, but if Tesla calms down the performance of thier transmission and motor for a potential Sedan version, it should get much better range than the Roadster does. That doesn't take into account any new battery tech that they could be using by then. A sedan would, of course outweight the Roadster and that would need to be taken into account as well.
I love the Volt concept, but I thought the idea was to get away from oil completely. To me, the full electric concept is more of a real answer to our oil dependency and much of the pollution problems of combustion engines. Isn't GM still behind the curve on this? By the time the Volt comes out, Tesla- and possibly others, may already be touting fully electric cars that can directly compete.
If the Tesla Roadster was more cost effective, there is no doubt the would be selling more than they could produce...wait, they already are, and that's at 100k.