If they say that it can't be bought, then they can't enforce copyright laws in the case abandonia has it for download, because abandonia has not caused them any financial damage...
But you don't have to prove financial damage to enforce a claim of ownership in a court of law--you only have to prove uncontested ownership. As an example, take the late films of Charlie Chaplin, from the 1940s onwards. He never released the rights on these after their initial screenings. He wasn't making any money on them as a result, but he (and later, his estate) quickly issued injunctions against any movie theater that tried to revive them. They were only shown again after the rights finally lapsed.
Mind, I'm not saying Lucasarts would automatically do that. But any abandonware board has to ask itself this question, when they go up against a multi-billion dollar corporation that protects its own copyrights eagerly: do you feel lucky today, punk?