I suggest that the core
I suggest that the core premise of your argument is wrong. You cannot make the assumption that "Most buyers of electric cars such as the Chevy Volt... ...can afford the vehicle without subsidies". In addition, I think you miss the greater point and intended benefits of a government subsidy such as those extended to these EV buyers.
Thanks to the available federal subsidy (plus an additional subsidy available in my home state of TN) my family is looking to buy a 2012 Chevy Volt. Without these subsidies we would never consider a vehicle in this general price range and we most certainly don't fit your assumed stereotype demographic of being a buyer with such means.
More importantly, you don't seem to recognize the real benefits of these subsidies to buyers (regardless of their financial means) as well as the American auto industry on the whole. First, it tempts the more able buyers to make a purchase which is beneficial to domestic manufacturers. Something many would likely not give much thought to at all. Buy American vs. the status building image of a German or other European maker? Second, encouraging EV purchases helps the automotive industry (and in this case the American auto industry) develop their product lines with an eye towards the future and a level of product that will likely define the future of that industry in the foreseeable future.
The government subsidies are doing exactly what they were intended to do, they are encouraging American consumers to make a purchase that will benefit the American auto industry, the American environment and the American family budget down the line. All good things, unless you happen to live off the back of the American oil industry I suppose...