There are web based IRC clients. IRC can integrate with other platforms pretty easily. IRC doesn't require setting up your own server.
Being able to setup your own server is a benefit, not a negative. Much like twitter it seems to be another regressions from an open internet to corporate control.
The only positive I can see is rich text, but that has extremely limited value in a chat program. History is nice too but IME too painful to use (scroll, load, scroll, load, scroll, load) to be of any practical benefit.