Sure, it's XML. And had I been the one to design it from the start, I would have gone with JSON. But come on.
RSS has been losing ground because, deep down, people love the algorithms. I personally hate how algorithms artificially mangle content that I would have seen anyway if my "timeline" was chronological; it's annoying to me to have stories from hours or days prior to appear near the top of my feed because everyone has already seen the same thing by now and new comments are worthless/unseen after a givens tory is ~1.5 hours old.