I heard Louis Von Ahn (Duolingo ) say that they spent $0 on advertising, which sounds great - users love it so much that it spreads completely organically. But in reality they must spend a lot on all the blogging, social networking, and community management - which sounds a lot like marketing to me.
I'm also a bit skeptical about Duolingo's ability to sustain itself selling translations, but I think it's possible, and the product is really great so I'm rooting for them.
Although it's scary to be in the same space as Duolingo, I don't see them as direct competition at the moment, since Duolingo requires users to be much more active in either completing exercises or translating everything, whereas Readlang is centered around the more passive activity of reading. In fact people regularly recommend Readlang on the Duolingo forums as a complementary tool.