While apparently successful in this case, that would appear to be a gross misuse of copyright and this layman would say that Blizzard got lucky and the judgement as precedent sounds fragile.

That's exactly the way GPL misuses copyright to enforce terms on people who have not agreed to contracts with the software provider.

Yes, it's a loophole in copyright law that can be used to massively expand it's scope. It is, however, well established in court.

I wouldn't agree with that characterization. GPL terms only apply to redistributors. If you receive GPL software, it's yours. It is only if you want to do something that copyright requires you to have permission to do that the GPL actually kicks in. If you never redistribute the software, the GPL actually lays zero constraints on you.

This is in contrast to conventional EULAs, which forbid you from using the software until you agree to them (basically forbidding you to "receive" the software), and forbid you from any form of redistribution. The case hythloday cites is a EULA issue.

There's nothing abusive about how the GPL uses copyright law. If you violate the GPL and redistribute the software anyhow, that simply means that you are redistributing software without the consent of the owner, which is a very direct copyright violation, not a strange penumbric emanation or anything.

And reversed on appeal: "To recover for copyright infringement based on breach of a license agreement, (1) the copying must exceed the scope of the defendant’s license and (2) the copyright owner’s complaint must be grounded in an exclusive right of copyright(e.g., unlawful reproduction or distribution)".