Wow. Didn't realize Animorphs were longer than HP. And I always say I don't read HP because it's too long
Yup, one method of improving the reliability of getting the response you want out of someone is breaking the task into smaller, descrete packages; Skinner observed it as well as many other response techniques in rodents. Its why you can eat a whole bag of potato chips when you would have been satisfied with a snack bar instead, the chips are so small it is easier to keep having "Just one more." Its also the reason for tiny levels in
New Super Mario Bros. Wii or frequent checkpoints in video games, so that you will do "just one more thing" before stopping. I don't think that the Harry Potter books could have been broken down at all, but it is certainly true that those smaller Goosbumps, Animorphs and other Scholastic books are a more reliable way to keep people coming back on a long term basis.
Anyways, I'm not sure I agree with the twice as awesome. Don't get me wrong, I love Animorphs, but HP was pretty darn awesome too, even if a bit overrated amongst the general public.