I don't know where you get your 99% number from? Some kind of study or something you could link to please? if I used my own observations when working for various organisations, I would say something like 100% of all companies have software developers.
Also, the "only" thing that matters? I have an idea of something that matters: the product actually doing solving the problem. I don't care if it was backed by Joe The Plumber or "Backed by the Full Faith and Credit of the Federal Government of the United States of America". If the product doesn't solve the problem, it's basically useless.
Regardless, FOSS is definitely preferable to proprietary. If all things are the same, if I could get Windows or Office for free and with the ability to modify and redistribute it without restriction, that would be much better than the current situation. That is unless you are into kinky finance/legal BSDM with your vendors (yes, it is a real thing). I won't judge you.