Where I am, we are officially 80% on Win 7. New devices procured in the last year are all Win 8.1 (15%). Remaining 5% (4.9% to be exact) are on other OSes like Linux, OSX. Which leaves XP, Vista, etc. in the 0.1% category. I suspect there would be statistical errors, but the overall picture puts XP to rest.
That said, it's usually the 0.1% that cause up to 50% of all managed software conflicts. Grrr...