Everyone dies because everyone loves Harry.
If you think about it, almost everyone that had like or loved(as a friend) Harry, had died
Not saying that it's his fault, but I guess Voldemort, seeing what happend to him 17 years ago, felt that anyone that loved him, would give up their love to him and protect him, like Lily and James Potter did 17 years ago.
I havn't read the book. I am reading all of them in chronilogical order first, because I need to freshen my memories. But I hear that the book was awsome