While there are only 13 authoritative
DNS servers, the reason they work is that DNS records can be extensively cached and you usually don't have to go all the way back to the root servers for that information.
It's also worth noting that routing, as it currently exists, only works well on hierarchical network structures. Packets go up the hierarchy as far as they need to in order to find a route, then they start back down again. This is the reason default routes are so important. "I may not know what to do with this packet, but there is one and only one guy I can send it to who I'm certain knows more than me," is how they work. Fully decentralized routing, in which there can be an arbitrarily large number of routes between any two nodes, is not a fully solved problem at this time.