But I do think it's ridiculous to expect the children of authors to profit of their parents' work after the author's death. Most people don't get to collect royalties for the work their parents did: are you paying a fee to the children of the person who built your house? Personally, I think cultural artefacts should be protected for twenty years or until the death of the creator -- whichever is shortest.
If the purpose of copyright is to enrich culture, then the ever increasing periods of exclusivity are very, very contra-productive. For instance, there are very few books that were new in the 1980's now available on Amazon. That's certainly not enriching the culture -- it actually makes the selection poorer. And as an author, wouldn't you want your work to be out there, so that others may enjoy it? So that they might buy your stuff?
A good example of a great way to 're-mix' cultural artefacts was given by today's Wondermark strip. Today's strip makes exclusive use of images released in the public domain by the British Library. Because the copyright ran out, the creator was free to re-imagine the images into another setting, and enrich our culture in that way.
Why do we have to wait so long before our culture becomes 'ours' again?