Reddit's a unique case because their initial user base (like News.YC's) consisted of other YC founders. And since they couldn't afford any form of promotion that cost money, news of the site spread mainly from those users.
I'm finding it difficult to square your assertion that Reddit is "unique" in this respect with the assertion that it's the web that's "making marketing and distribution free".
The only way that web marketing is "free" is if product awareness spreads between customers, or is pushed through the founders' personal contacts. Wouldn't this imply that we could expect this phenomenon - the initial user base being in some way close to the founders - to grow as the industry approaches the asymptotes you assert it is heading for?
And other followers of your essays, and people who got rejected from YC that first time. I checked out Reddit at first because I was curious what the folks who did get in were up to. And they happened to have built something cool, so I told a lot of my friends and family, and who knows who else they told.
I think it's a fairly good bet that Reddit did a lot better with their initial group of users being seeded from folks who'd heard of you or followed comp.lang.lisp, than if they tried to launch something among their UVa friends.
