I use Windows at work, because work says I have to. I have a Windows 7 laptop loaded down with management agents and security agents and update agents and all kinds of other agents, which makes IT security comfortable. If I wiped it and loaded Linux, or God forbid if I brought my MacBook from home in to work, my network port would be disabled within seconds and I'd get a fun walk-up visit from security a minute later.
My job requires me to shuffle around MS Office documents, do e-mail, and use web-based tools. There's nothing there that can't be done on another platform, but Windows lets my work keep tight, locked-down tabs on my laptop. The need for that control is at least in part driven by the vendors selling those lock-down solutions. There is a fear- and risk-management-based culture in IT security these days, and Windows is the platform that has the tools that companies have been told they have to deploy to keep things safe.