At PHP, that age-old issue of the Harry Potter books having many details similar to other fantasy sagas came up again. Some literary critics have used this argument against JK Rowling and her highly successful series, saying that she's taken many elements from other fantasy series like Lord of the Rings, and incorporated them into her stories. People have pointed out parallels between Aragog and Shelob, The Mirror of Erised and The Mirror of Galadriel, The Whomping Willow and the Ents, Dumbledore and Gandalf, etc. Even though this has been debated to a pulp, I'll put in my 2 sickles before burying the topic.
The fantasy genre is one that is based on imagination, and even though an author's imagination is limitless, somehow, the genre has many many common elements across all the different stories comprising it. Dragons, wizards, magic, fantastical creatures, heroic feats, good versus evil, these are elements that you will find in most fantasy stories. The patterns date back to the early mythologies of the Greeks, Romans, and even the Egyptians. Fantasy is an unreal world, a world of the unfamiliar. But these common elements give readers a certain familiarity with the genre that makes them feel right at home with the stories. The same elements combine in different ways to form a different story that remains recognizable.
In my humble opinion, this doesn't mean an author plagiarized another author. That just seems to be the nature of the genre. For if we say that the contemporary authors took their ideas from the classical fantasy authors, then it is also safe to say that the classical authors took their ideas from the works of the ancient mythologists. But that is not so. Somehow, Fantasy has become every reader's and author's common dream, a common product of their collective imaginations, a common place to escape our real world.
With that said, I've found that I've been able to appreciate Harry Potter, Lord of the Rings, Dragonlance, and the other stories of the genre, independently, treating them as unique worlds, and revelling in their unique perspectives of the common elements of Fantasy. :) The more worlds we have to enjoy, the more we learn, and as in all literary genres, those seem to be the objectives of reading. :)