Zombies and vampires - variable canon?

[Argh]

I heard some strong opinions from a niece about two recent movies and was
curious as to how reasonable her assertions were:

http://www.zompiredraculariussocietyofamerica.org/

While neither movie appeals to me (being an old geezer who is looking more
like a zombie himself with every passing day) I was mostly curious if the
Twilight movies aren't considered decent vampire movies because of their
alleged violations of long held vampire canon.