Is it really? Scaling today means running on more than one machine (google, facebook, twitter, etc.)

That means no shared memory. He helpfully makes this distinction on his front page ("I'm mostly interested in shared-memory system, so if you are looking for information about clusters, web-farms, distributed databases and the like, it's the wrong place")

According to Google's Jeff Dean, "to Google, multi-core computers look like separate servers with really fast interconnections" (i.e. memory).

So if you are running your applications on many machines anyway, you might as well drastically simplify your code by writing it "single-threaded" and running #cores copies on each machine.