What a great post! I always wondered if J.K. Rowling decided several books in to redeem Snapes, or if she knew from the very start that this was the direction he was heading. As an author, I couldn't allow him to dish out all that verbal abuse. It's a weakness of parents and writers alike - this desire to protect our protagonists and our offspring from suffering or from being hated and misunderstood.
Now, that song... phew! - I was worried it'd stick in my head if I dared listen, but it has none of the "stick" factor that Dr. Horrible has (the Whedon brothers - so addicting, I bought the DVD and the CD!).