I've likewise had a lot of variation from big corp to startups in companies in different sectors, and it seems to really depend on the org and what platform their managemetn likes. Windows companies usually offer a choice, but if management likes Apple then it's so common to get forced onto a Mac (and often with a dismissive "nobody wants to use windows" comment which really pisses me off). There's usually a small population using Linux if they can get away with it. When devs are given a truly free choice (with no cultural pressure) between windows, mac, linux, a relatively common split I see is about 40% linux, 40% mac, 20% windows.