As far as I know (which isn’t perfect knowledge by any means) MS has had a hardware division since 1982, it’s just that it was never their focus. IIRC Bill Gates famously didn’t want to become a major hardware vendor, but wanted to focus on the software. Certainly I’ve never heard of a ban or anything like it, and I was under the impression that dealership laws were essentially unique to cars. If you have some other information to the contrary I’d be happy to read it. Obviously if such a ban existed it was lifted before MS made things like the Zune, or Surface.