This sort of thing doesn't really mean very much. Language choices for start-ups (well, B2C social SaaS apps really, because that's what "startup" appears to mean these days) tend to favour real-time non-blocking connections that scale easily. That essentially rules out PHP unless you augment it with something else (a small node.js server, Pusher, etc). It doesn't mean, say, that PHP is a "bad language". It just means it'd be an inappropriate choice in that instance.
If the next intake of YC hugely favoured chat apps, we'd probably see Erlang as a really popular language. That doesn't mean you should write your blog software in it.