Whether or not the Volt sells in mass quantities, the importance of it is to improve GM's public image. To a large portion of the public, GM is the builder of obese, gas guzzling trucks and SUVs, the company that 'Killed the electric car'.
Toyota has the green image sewn up these days, Honda will probably make inroads w/ the new Insight. GM wants to improve their green image. The Volt is the anti-HUMMER. If the Volt can help improve GM's image, and GM is able to still make enthusiast-appealing cars like the Corvette, Camaro, CTS, etc, then that's progress...