All of those systems apart from IM follow the same route to success - a large number of independent systems with a common interchange format that makes it possi

All of those systems apart from IM follow the same route to success - a large number of independent systems with a common interchange format that makes it possible to create the illusion of integration. Every mail server, every news server, every blog is a little island that runs on it's own. I would bet that behind the scenes even the big IM networks are actually a mountain of small, effectively independent, service providing systems that understand how to talk to each other - that's certainly how the XMPP/gTalk network functions. This is only possible because all of those designs are fundamentally highly parallel - if your communication method has data dependencies (real or the result of bad design) that cannot be managed in that way then you get something that won't scale.