They are severely fragmented from the main network, which usually has several thousand clients on simultaniously. When this happens, try finding another host. You don't need to disconnect from the first, you will just likely get a larger network using another uplink. GnutellaNet works on a very different principle from most other networks. It is called peer to peer because that is how connections are maintained and data is passed.
Most internet protocols rely on a central server to connect the other parties to each other.
This is not the case with Gnutella, where there is no intermediary. Data is passed along the network from client to client directly. With the exception of file transfers, which are a direct link between you and the other host, all data travels everywhere. Your search results are sent through other clients connections as well, but they can't see them due to the anonymous GUID Gnutella assigns to each search. Sorry, I only have a functional understanding of GnutellaNet, I am no expert by any means.