Humans work well with ambiguity and context. You know that when your coworker says "Bob's birthday is this weekend" you know she means her husband Bob, not Bob from accounting who nobody likes. And you even prefer that system to having an unambiguous human identifier, even a friendly one like "Bob-4592-daring-weasel-horseradish".
Machines, on the other hand, hate ambiguity and context. Every bit of context is an extra bit of state that has to be stored somewhere, and now all your results are actually statistical guesses - how inelegant!
In the early days of computing, there was no separation between the internals of the machine and its interface. If you worked on a computer, you were as much the mechanic as the driver. We got used to usernames, filenames, and hostnames because they were a decent compromise; they were meaningful enough to humans, and unambiguous enough for machines, so we could use them as a kind of human-computer pidgin.
But we don't need them anymore, and they were never really very good at either job anyway. Google's (probably accidental) discovery was that we were using the web wrong. Everyone was building web directories and portals because they thought that URLs weren't discoverable, but the real problem was that they weren't usable. Search was the first human interface to the web.
So Google's going to kill the URL, Facebook's going to kill the username, and someone (apparently not Microsoft) is going to kill the filename. There'll be much wailing and gnashing of teeth from the old guard while it happens, but someday our grandchildren will grow up never having to memorise an arbitrary sequence of characters for a computer, and I think that's a future to look forward to.