This is a myth. And people will realize in a couple months once there are tons of apps in the App Store. You will need marketing wherever you go. For word-of-mouth, your app needs to be really stellar. And that is true, everywhere.

I suspect the more appealing part about the App Store is that more people will want to actually pay for your app right away if you provide them with enough quality. It feels like the expected payoff with the App Store would be higher for individual developers this way as opposed to making viral apps on facebook and monetizing via ads.