Internet Relay Chat is THE archetype of chat protocols. It has been around since the early days of the internets. Hence the protocols and software are mature albeit with some flaws or restrictions that are hard to come by.
Google Talk is using XMPP, an XML based presence and chat protocol that has also been there for quite a while. It is widely used throughout the net apart from Google Talk.
So both protocols serve their purpose well. IRC is a little more focussed on group chats. While one to one conversations are simple, a presence service is not what IRC was made for. XMPP is strong on presence and one to one chats, with less focus on group chats.
Google Talk is using XMPP, an XML based presence and chat protocol that has also been there for quite a while. It is widely used throughout the net apart from Google Talk.
So both protocols serve their purpose well. IRC is a little more focussed on group chats. While one to one conversations are simple, a presence service is not what IRC was made for. XMPP is strong on presence and one to one chats, with less focus on group chats.