There are a whole host of reasons to use one OS over the other but this "Free as in Speech" is simply not a very good one. I'm far, FAR, more concerned about "Getting Shit Done" than I am about the free-ness of my OS. For some tasks the right tool for GSD is windows, for others it's osX, and for still others it's some Linux / *BSD (I'm a NetBSD fan myself).
It seems short sighted to say that some arbitrary and subjective personal belief system about technology makes one system inherently "better" / "superior" to another. I guess it's a matter of what sort of things you grade on, For my personal OS grading metric there is only one item, "Helps me Get Shit Done". Nothing else matters, I just want to be productive.