Since you probably missed Harry Potter because of it, I am going to claim that you miss some good things with the heuristic. On the other hand there is doubtless a lot of crap that is popular.
Would be interesting to see some statistics, but maybe people have to do that on an individual basis.
I think a big part of it is that I really don't like discussing books/movies with other people. I know that is odd. I just like to have the story in my head and interpret it as I please, without having to hash it over with everyone else in the world.
It's paid off for Harry Potter. I get perverse enjoyment out of rejecting my girlfriend's sister's desire to discuss whether such and such character is in love with such and such other character. Since I haven't read it, she won't ramble at me for more than a couple seconds. I fully plan on reading it someday, once the furor dies down and there is no risk of having a coversation about it. ;)
Weird, I would never miss a chance to read a book that compares to another favorite book of mine.
I have noticed the similarity in themes, too, but I have enjoyed both Harry Potter and Enders Game. They are not similar in the sense of being clones. Also, the "flying game" is only a side plot in HP, and was for me the least interesting aspect of the books.