Hmmmm, Ok, not sure why I haven't noticed that in Windows. C3 does match that. Regardless, if you lookup any of the millions of application UX design guides, patterns and practices, they will all say buttons should be recognizable as a button and should indicate what the button click does. So they're actually incorrect in Windows too :-/
Unless...
There is some established design (that I haven't seen so far) that says UI expand/collapse arrows should be reversed?