I run a jabber server. If you look at the implementations
you will find that they still work as hubs for connected
users. They are not point to point.
But unlike AIM or MSN, it's a distributed model, not a single
monolithic setup. And in reality, it isn't infeasible to make it point
by point by building a jabber server into every client, where with AIM
and MSN or yahoo chat, that's not possible.