It's interesting to exchange these retorts with you.

We really have completely different views and probably (and 50% is certainly on me) trouble understanding each other.

Microsoft was (is!) a monopoly. Although you can buy OS X, get Linux, FreeBSD, OpenBSD, NetBSD, Nexenta, SmartOS, Solaris, Haiku-OS or whatever floats your boat. [1]

Facebook is a monopoly, even if there are products/services available that provide something kind-of, sort-of similar.

1: Apologies for missing someone's favorite alternative OS in the list