Some games like Dust have exploded in popularity through word of mouth. For the PC release, I'm sure Totalbiscuit sold thousands of units by himself.

In the PC ecosystem it is actually much easier to get by without advertising because this article does get something right, that if you can get the game in front of the right people they will advertise it for you through the youtube gaming scene at al. Look at Minecraft and how much advertising it had.

It just has to be insanely good and innovative enough to justify people giving a shit to spread it like wildfire, rather than play it as a weekend hobby and forget about it.