There's a lot more to an operating system than how it manages non-fullscreen applications. "Windows" is obviously a related term, but I don't think it's generic--when I boot up Linux on my laptop, I don't say, "This Linux/Xorg/Openbox combination sure is a great windows!" But I might say, "This collection of software for my smartphone compiled and sold by Amazon sure is a great app store."
Edit: See also: MS Office, MS Word, MS Security Essentials, and arguably MS Internet Explorer and Windows Explorer (I browse the internet and manage/browse files--there's not much literal "exploring" going on)
> I don't think it's generic--when I boot up Linux on my laptop, I don't say, "This Linux/Xorg/Openbox combination sure is a great windows!"
You never 'open a window', or 'close a window', or 'change a window'? You might be younger than me (I'm 30) but I've been doing that since having an Atari ST in the last 80s.
As far as I know, MSFT doesn't have a trademark on the term "window" as used to describe objects in a GUI. They have a trademark on the term "Windows" as a whole system.
Same reason you can buy "linux" laundry detergent.
I'm going to flat disagree that windowing systems and window UI elements are separate fields of endeavor, in the same way that laundry detergent and computer Operating Systems are. I think most lawyers would too.
Edit: See also: MS Office, MS Word, MS Security Essentials, and arguably MS Internet Explorer and Windows Explorer (I browse the internet and manage/browse files--there's not much literal "exploring" going on)