The size of the network and how much time opers have on their hands has nothing to do with it. It all comes down to one thing and one thing only, the ability of server software to allow spying on private messaging. There's hundreds of networks with less than 500 concurrent users where this would simply not be possible unless someone with programming knowledge modified the software. The network I use has between 500 and 1000 concurrent users, still could be called a small network going by those numbers and we use commercial software - read: spying on private messaging is not possible on there.
Catagorising networks the way some of you have simply hinders the growth of small networks and nothing else.
