A Quick Rant: School Library Journal, what were they thinking?

        For the last few days after school has started, I decided to get a jump on reading "Tween" Lit and sticking to the "Independent Reader" category in the bookstore. However, since I absolutely loved the Percy Jackson series and have already read all the Harry Potter today, I decided that I would give the Heroes of Olympus a chance, which is absolutely fantastic, I am almost done. However, today, I went to the library for another class and was glancing at the "independent reader" section in the library. At the Newport Beach Library, most of the "independent reader" category is mixed in with the children's section, which is okay, reading up is always alright. However, Harry Potter was in the children's section of the library which was actually surprising. However, then, I decided to look for Riordan in the same section, however, there were no Percy Jackson, Kane Chronicles, or anything. Having a hunch, I checked on the computer. Harry Potter is categorized as children's books but Percy Jackson, Kane Chronicles, and Heroes of Olympus are not. This does not make any sense to me. Harry Potter is a wonderfully dark tale. However, I am talking about DARK. There is torture, death, abandonment, child abuse, plotting, wars brewing, and sacrifice, this has extremely adult themes. However, with Percy Jackson while good the writing is not at all as mature as Harry Potter. 

After my trip to the library I decided that I would look on Amazon and try to figure out the motivation. According to Amazon, the School Library Journal rates Harry Potter 3rd grade and up, while Percy Jackson is given a 5th grade reading and up. This to me makes no sense. There is death in Percy, do not get me wrong, however, the only thing that I could fathom would be is the slight more emphasis on teen romance and the theme "that gods were promiscuous with mortals and produced children." There is some more kissing in the Percy Jackson series and a lot more touchy-feely scenes in the Heroes of Olympus, however, I just don't get it. Thoughts?