A google search reveals a considerable number of hits, with a high consistency of email sig line repetitions attributed to Linux supporters/users.
I’m willing to bet the quote originated from someone who dislikes Microsoft and prefers Linux, all other things being equal. I think the serendipitious approach where the quote seems to dovetail nicely with the perceived arrogance of Microsoft lends a false credibility that Microsoft wrote it for the company.
Is it possible that the Microsoft marketeers wrote it? Well, anything is possible. Are they arrogant enough to write it, knowing how it will be perceived? Well, anything is possible.
Only the real author knows for sure. Don’t bet he/she will admit to it, and if they ever do, they will be believed by anyone.