Yeah, we actually have an organic view of the system. You could crawl the entire network/graph you are on, given enough time (yes, that's cheating, but give me a minute), but you will never need to crawl that entire network because useful information tends to cluster, and nobody needs _all_ information, but rather _useful_ information. It's more a question of finding the appropriate jumping-in spot and exploring in a radius from there.
This is essentially different than a centralized database, where you are forced to ratter through all records, until you find the appropriate one, so that having lots of records destroys efficiency or even ends in a time-out.
Furthermore, we expect similar information to cluster more and more, over time, so the need to crawl the system will diminish over time, despite the total amount of information increasing.