What is actually happening is that real people are not chatting as much as they used to and the spots are being taken by bots that distribute wares. Many of the networks with anywhere between 1 and 5000 users are networks with a dominant filetrading population. They are not real people and contribute nothing to what IRC is meant to be. One network has truly prospered as far as it's usercount goes and that is Quakenet, though much of this increase will be the wares groupies that Dalnet no longer allows. Proof of what I say is in the pudding. On that website Starbucks quoted you will see a top 30 channels. At best, one or two will be community chatrooms, the rest is wares, wares, wares.
Personally, I think it sucks. I am not necessarily against the principle of 'try before you buy' but the trouble is, those that frequent these popular channels never get to the 'buy' stage, rather they use IRC to leech files which are often laced with trojans and other dangerous data. As ar as real people go, IRC is in a state of decline. Whether it is a permanent downward spiral or not we will have to wait and see.