They're not going to do that. Their lawyers would beat them silly for "giving away" intellectual property - whether they ever intend to use it again or not. That's why these things always seem to be a grey area. They probably don't really mind, but they cannot formally condone it. If pressed for an answer,  they'd say "no". That's (for better or worse) the modern legal landscape - if you don't fight to control your IP, somebody else will exploit it and then you have less say because you didn't defend your ownership. The only way such companies could get away with it now is to pass it on to another small company, like a foundation they started. I think Sun did this with OpenSolaris before they were acquired by Oracle.

Small companies are more likely to be explicit in declaring things abandonware, because they aren't as beholden to investors and legal teams.