Storytelling

I have several cartoons pending, but overtime at work, unexpected delays, and the new Harry Potter book are slowing me down.
I think the Harry Potter books owe much of their success to J.K. Rowling's ability to tell a good story. Even before the last book was released she hinted that she'd kill off more main characters, possibly Harry too. That's good storytelling. Even before you open the book you're thinking: Who dies? Does Harry get killed? How? When?
Compare her to a lesser known storyteller whom who recently announced who he was going to kill off and how it would happen. Why the specifics? Who wants to read the series if we already know who gets killed and how it happens? I don't get it.