Heh! It's so true. But it's not like it's bad that Snape's thick cardboard because he works. I think it's in Orson Scott Card's book about fantasy writing where he says that in an Event story (which is what this is) character "development" isn't always necessary. There's a difference between development of character and creating memorable characters. Snape just has to be Snape and stuff happens. He doesn't have to be overly complicated or change over time. In fact, most theories that claim he's going through all these changes I think make the story weaker and not stronger.