Thanks a lot for the post.
What suprised me the most was the fact that Google is serving 40K (now 47K in live statistic) requests per second.
That was way below what I thought.
Each Apache server without real optimization running on a typical physical machine would be able to serve 40-50 requests/second; so they only need a thousand of servers to do 50K requests/second.
Or am I missing something?
Your missing factor is "the fact that Google is serving 40K (now 47K in live statistic) requests per second" is wrong.
"The number of requests peaked out at 52 Mbps. Let’s put that number in perspective". Perspective is 52 Mbps isn't a small number, but not massive either.