It is about getting staff to support your business, and the software you need.
If you have a Linux shop, you need to find people with Linux experience to keep your company going. These people with Linux experience also know Windows. However you need to find people who know Linux well enough as there is a gap in skills between very basic user, and administrator. For windows you can hire most any tech at any price range you need. You need a $10.00 per hour kid to make sure the disk doesn't get too full and install software, you can find some one. You need a $50.00 per hour skilled admin who will operates complex networks and mass storage you can find them too.
Next is software. You don't work in a vacuume your software will need to work with vendors and customers. That software you need for your business might have a Linux port, but there is always a windows version. You call for support you say Linux they say sorry you are on your one.
The issue of hardware. Your Linux experience is based on the hardware you get. Get the wrong hardware it runs like crap, get the right hardware, Linux runs like a champ. Companies like Dell that sells systems preloaded with Linux are risky because the don't really give you a good compatible system. You need to spec out each component. Windows has the drivers and they work. Thus getting a Windows system much more reliable.
Often the cost of a system with or without a windows license is verry small, get the license you can always go to Linux in the future. When you are in the future, you have a windows infrastructure that is too costly to change.