That's a fantastic selling point in itself, and while I believe Toyota is trying to make another plug in Prius, it's 15 mile battery range is hardly worth it.
Additionally, the Volt is just a roomier, better riding/handling, and more comfortable and refined car than the Prius. The engineers apparently put a lot of effort into the "driving experience" aspect. If one drives them side-by-side the difference is totally apparent, IMO.
I always know I'm in for a fun trip when I get in the Volt. I can't say I'd say the same about getting in a Prius. GM's strong point at the moment is making hybrids that Americans would actually enjoy driving.
GM does currently have one pure electric offering, the Spark EV. They're only available in limited markets, however. They essentially just took the drivetrain from the Volt and crammed it into that subcompact, added a ~100 mile battery and a 15 minute charging option, and there ya go.
Though it's sort of a hack, it's actually not half bad! Around
400-something foot/lbs of torque off the line, same as a Ferrari 458. A cute "sleeper" that you can lease for a song, in the states where it's available.