I think it is great that an original author is planning to redo one of his old games for the current market. The problem here is as I see it is that there is nothing illegal about the new engine, just like there is nothing illegal about ScummVM. If legal threats were made for the sake of "protecting copyright" or whatever, the author of this new engine could tell them where to stick it - and rightly so. But it seems it was made as a polite request because they were already doing something similar. Since this two-way respect never seems to happen nowadays I applaud the actions of both parties in such a "difficult" situation.
I certainly wouldn't call the author greedy. It *is* his game after all, and in my country it will remain his game for the rest of his life. Tom Jones still receives money for songs he released 20 years ago doesn't he? Why should games be different?