I don't think the main problem with Windows PCs is the cost of AD/Exchange/etc although it's a big problem. IMO the main problem is that even well managed Windows installs have a way of turning to shit (mine did recently). OTOH ChromeOS is the exact opposite: unless you put your Chromebook into developer mode you cannot muck with the OS at all. And even if you manage to somehow get your device into a bad state, reinstalling from a factory image is easy. So Windows might have more apps and be a more capable OS than ChromeOS but its support costs are too high for it to viable.