Trivia: There is, in fact, no single author for the Warriors books. It's about 4 or 5 women all writing under the same pen name.
And like all shitty young reader/teen crossover crap, yes...the majority of the buyers and readers are well over the intended age.
Which says something about society or something I guess.
Apparently there's enough people out there who will argue that as an adult who reads juvenile or "Young Adult" fiction it simply means they are more "open minded" and don't let things like target age groups prevent them from going on wondorous literary excursions - usually in defense of slobbering and writing shitty fanfic over the latest Harry Potter or Twilight-wannabe series or what have you.