As a foreigner, I won't be able to afford an EV for along time but I think this makes it more likely I'll get it sooner, due to the technologies proliferating.
On the specific issue, they have to start with a narrow market and high cost. Classic crossing-the-chasm stuff, or Porter's differentiation strategy focusing on a different market segment than the Prius. They've changed the perception of EV's, making them desirable where alternatives were ugly tradeoffs that screamed "bunnyhugger". You couldn't get me into a Prius, but I'd really like a model S.
I suspect Mr Musk would have done just fine without government support, but I'm sure it's helped a lot.
Not that your point isnt valid as well, I imagine that they see it as a welfare solution on the bottom end.
$15,000 would buy outright a decent car with good mileage for someone poor but responsible who couldn't get to work otherwise.