The basis IIRC, was an antitrust issue. Remember the Fairchild 9440 CPU--the Nova clone? Fairchild joined with Digidyne in a suit against DG. The gist was that since DG sold RDOS separately (non-bundled) with their hardware, denying software sales to non-DG hardware users was an attempt to unfairly exercise monopoly powers.
I don't think the matter of hardware cloning was being contested. After all, there were plenty of S/360 clones out there (e.g. Two-Pi systems, RCA, etc.)
The Supremes eventually sided with Digidyne and both Fairchild and Digidyne collected damages something like 10 years after suit was first brought. The wheels of Justice grind exceedingly fine and exceedingly slow. Since anti-trust cases are almost a relic of bygone days, I don't know if Digidyne v. Data General holds any legal sway (IANAL, much less an anti-trust specialist) today. But it was a big deal back then and followed by a lot of people in the trade.
Maybe one of our legal scholars can comment...