The thing is, IRC is tried and tested. IRC has developed ways to combat spam, abuse, irritating kids, etc etc. That's one of the things that makes it more attractive than any new solution. And of course it's easy to write bots for.
I know I'm biased, but I expect IRC to have a real surge of growth the next year or 2, and take over somewhat from other less immediate forms of communication.
Massive growth from video streaming/chat sites - ustream, justin.tv, things are only going to get more real time interactive, and people are likely to go with IRC.
It actually predates the web, by just a little bit.
Personally, I see Jabber having real growth within the next 2 years due to GTalk, Facebook Chat and MyspaceIM. And as with IRC having a pretty interface, a multitude of people using these means of communication have no idea they're actually on a Jabber server.
Go figure.