There's loads of issues with IRC though. The client issue can be solved reasonably easy with an applet or something, but then there's finding a suitable network (unless someone already knows of one), there's netsplits, there's the learning curve (might depend a bit on the client), there's... well, a whole lot.
The current solution (99chats) isn't much better, admittedly, but IRC isn't as good as you make it out to be.