It's simply an extension of regular copyright law (yes, I know that the law does not apply directly to mods due to the EULA; that does not mean that the reasons why such laws exist are not relevant) to say that the creator of a work has supreme rights to it, rights which are not waived simply by silence.
Silence does not equal consent, in this or any other case.
To continue with the use of your anology:
Copyrights eventually revert to public domain, despite corporate big bucks political clout which has extended many copyrights of late.
It seems to me, at least, a discussion of a cautious and respectful equivalent version of public domain for mods is very appropriate in this specific forum.
However, as strictly a mod user myself, I do have my own dog in this race. And I would dearly love to see some of the older mods cleaned, pyffied, debugged, and polished.
As for silence, isn't the only thing it truly equals........... is silence?
And while saying all this, I do admire your and others adamant efforts to defend the rights of mod makers.