I don't know about you, but when I go to TPB, I'm not greeted with a bunch of pages with nothing but simple low numbers. I'm greeted by a search engine, which shows me great lists of things by TV show name (for example), which I can click on and get taken to a page where someone describes what's on offer with this 'number', and other people comment on the quality. I can get the torrent hash, and also instructions on what to do with it. It's generally not something that needs to be verified very often, either.

And in any case, if someone says "hey, where can I get meth", and you say "42, just deconstruct the number with this algorithm", you've done the same thing as just handing over a phone number - you've facilitated the contact.