Daniel Pinkwater once told me he learned all he needed to know about books and their function for young readers by reading the letters to the editor of Batman comic books from the 1940s. Every letter, he said was a variation on "I'm 8, and my brother Sheldon is 4. Can you have Batman beat up a kid named Sheldon?" In other words - it was all wish fulfillment.
This is certainly true in modern YA. The field these days revolves around books where the girl (who readers are supposed to think is just like them) loving her first boyfriend forever and ever (despite one of them having a terrible secret). I'm a bit disturbed by the letters I get from girls who read I Kissed a Zombie and I Liked It and write me or leave comments saying they wish they had a boyfriend like Doug who loved them even though he was dead.
It seems that Charles Dickens, who turns 200 today, got letters not unlike the letters that the editors of Batman got. In 1841, he wrote a letter in reply to a kid who'd been reading Nicholas Nickleby and apparently asked him to beat the heck out of Wackford Squeers (sort of the 19th century Dolores Umbridge) and give Nicholas and his friends some money and sheep, plus a nice meal of roast lamb and porter (the kid seems to have liked sheep, both to own and to eat). Dickens' delightful letter in reply to the kid is reprinted in today's Letters of Note.
Happy birthday, Dickens!