Video and audio support is not necessary. In fact, it would ruin mirc/irc. There are other kinds of chat systems where one can chat via webcam or mic, irc was never intended for such purposes. It's as simple as that.
If that makes irc/mirc archaic, then so be it. There's really no point in trying to update the irc protocol to include features it was not designed for, it would probably be a haphazard patchwork and would most likely suck. So if you want the "cool" new features, use MSN/AIM/whatever, and leave the boring old irc for us as it is.
