*for a corporation. For a single user who knows their way around a Windows machine, they are not.
Perhaps, but that's just the best case situation. I know my way around Linux, and that's cheaper than Windows on the individual level, and far far far cheaper than Windows on the enterprise level. All it takes is users that know their way around Linux, right?
The real determinant though will be the cost averaged out over skill levels and prevalence of skill levels.