It's not as straightforward of a choice as it may seem. In theory Linux would be a better choice but there simply isn't the infrastructure or IT staffing in place to manage millions and millions of Linux desktops. I'm not saying it can't be done but for various reasons it hasn't been done and that's a major practical roadblock. Just from a staffing perspective alone if you hand millions of Linux desktops to life long Microsoftsies you're begging for disaster.