Earlier quoted context omitted.
Okay, but why does it benefit Facebook's bottom line (and Google's!) to open-source that stuff? Wouldn't they be better off if their competitors had to pay those higher costs? It's not as if they have substantial computation-service providers they're buying from, or data-center-oriented companies they're selling to.
Releasing information about this helps others better compete with Facebook's competitors while not diminishing the value of Facebook's core asset at all.
Was anything mentioned about the OS running the servers ? I presume it is an optimized linux, but who knows.