Other way around. Those with a Windows domain tend to have *fewer* users because the admin chores are actually worse for small businesses when they add a new machine.
Medium businesses are pretty evenly split between having a Windows domain, having *some* of a Windows domain (file shares and access controls but no AD), and having no Windows domain.
You’re telling me there’s more maintenance involved in maintiaing a Windows domain than to duplicate users and passwords on every machine in the workgroup? Is everyone logging in as Admin?