You have to remember that just by being a person who read Hacker News you are not a regular person. I really don't mean to be harsh, but it doesn't much matter what you prefer or that you find this trend of running things in the browser problematic. What matters is what normal people do. People who don't even know what a "client" in computer lingo means.

Those are the majority, and if we want them to use Free and Open systems (which is my whole point here), then we have to create those systems in a way normal people will start switching from the closed systems and over to the open ones. And that is only going to happen if the open systems are easier to use and more accessible than the closed ones.

I am aware of the fact that Facebook uses XMPP (I mention it in the post). Still, extremely few people use it through a client. They use it through fb.com.