Yes, they're running Windows, and Windows is also software, contributing to the bloat. My point is that the resource overhead of just running an idle OS doesn't need to be humongous compared to the actual workload.
Seriously, they could be running on thin clients like a chromebook. No need to give everyone top-end machines to run MS Office and some webapps. It's mind boggling this is even a debate on HN.
But then they wouldn't be able to install the corporate spyware that keeps the evil hackers away.