You need that something else. Advertising alone doesn't help if the game sucks.
I do think this is true. Even in the commercial game industry, you can hype something all you want, but if the game sucks and the reviews show it, sales will drop off rapidly. Daikatana is a perfect example. Awful game, horrible reviews and it sold very poorly, despite massive amounts of marketing.
I just think the reverse is true, too. There can be an absolutely amazing game with great features, but without advertising no one will know that it exists. The game doesn't help if the advertising sucks or isn't there. In the case of DF, they got a lot of advertising through the SA forums and other associated high volume forums. I think DF is used as an example a lot because Toady is making a lot of money in donations. But I think this has more to do with a handful of consistent high dollar value donors, rather than the total number of DF players.
For me, Underhall received a ton of downloads when the 7DRL completion thread was at the top of r.g.r.d, and while Underhall was listed as a recently updated roguelike on Roguebasin. The moment that those two ended, so did the downloads.