The Wikipedia article doesn't make it obvious, but even Munich itself wasn't able to migrate everyone off of the MS stack. One of the linkrotted sources (https://web.archive.org/web/20180516042059/https://www.techr...) says they had about 17% of computers running Windows after the migration "completed" because some required programs couldn't run on their Linux distro. It's not obvious whether the working model was that 17% of staff used Windows exclusively or all staff had to find a Windows box to do some of their work, but either one sounds pretty obnoxious to me.