At the risk of sounding like I'm defending the Twilight Saga (believe me, I'm not), there are
different, legitimate interpretations of vampire and werewolf lore where the vulnerabilities you are discussing don't necessarily have to be present or not.
Example: On Buffy The Vampire Slayer
(the television series), vampires turn to dust when beheaded, staked, or set on fire. Vampires though don't sleep in coffins ("It's a myth!" says Angel).
On True Blood
however, some vampires do
sleep in coffins, or under the floorboards, and they explode with bloody organs and entrails all over the place.
Seemingly in the Twilight
films, they shatter as if made of ice or some other weakened stone.
I guess my point is simply that there's room for all kinds of interpretations about the mythology surrounding these types of characters, so hinging your whole reasoning for not liking the films or books on it seems ... well, uninformed.
Think about it.