Good point. Harry Potter is about a friend group fighting evil in a world of magic. If there is no magic, if in fact that world is less magical than the real world, then a big part of the appeal of the book will be lost.

Magic is not a big part of Shakespear, and the part that is (Ghost, fairies) are most dissimilar to the magic we have since created.

I also think that Sherlock will continue to remain popular because the appeal of the stories - who did it and how did the detective figure that out - has not fundamentally changed.