It's "funny" how a company that has built an empire on ransacking the public domain and obtaining the rights to others' work is so concerned with protecting their own work. Not that I don't understand the desire to hold on to what they have - but again, what they have largely came from elsewhere!
For instance, I know of a "Mom & Pop" shop owner who had his windows painted with Disney characters. He received a "cease & desist" letter from the Disney corporation. The "corker" is that he'd had them painted to promote the fact that he had their officially licensed party goods of their latest movie in stock.
How paranoid are we, anyway? It's bad enough that we speculate on the morality and behavior of authors past from shreds of evidence. Do we have to have such a clause as this one?