So it outsold the 7-series (top end full-size full-luxury sedan), the S-class (top end full-size full-luxury sedan) and the Audi A8 (full-size full-luxury sedan), which even BMW, Mercedes, and Audi would admit make up a small fraction of their overall sales, and this is a win?
The Model S is a top-end full-size full-luxury sedan. It makes complete sense to compare it to the top-end full-size full-luxury sedans of the incumbent manufacturers.
When you outsell the 5-series, the E-class, and the Audi A6, then you'll have something to talk about, as all three manufacturers sell an order of magnitude more of those.
The fact that they were able to outsell any manufacturers in any series during their first attempt at a car in this class still says a lot. Given that this is their second success (the first being the Roadster), and that each success is building on the last, I think that the future of Tesla Motors is very bright and judging by the stock price, so do many others.