I've noticed that too. In fact, even the trappings of religion don't work anymore. How many vampire movies have you seen in which the villain is shown a cross and simply slaps it away? Or when he actually enters a church and commits his foul deeds before the altar?
Not only do such portrayals reduce religion to a pathetic, ineffective institution, they belie the entire myth. Vampires are soulless; that's why they have no reflections in a mirror. The Cross is a reminder to them of their utter damnation: to wander the earth eternally, forced to find their sustenance in the lifeblood of others, yet to no ultimate end. Since they are not really alive (they are the Undead), they can never really die. Yet since they are soulless, they can never really live.
They are an abomination before God, and He will not suffer their presence. Nor can they tolerate His, in any form. The notion that one could ever enter sacred ground is absurd.
I once saw a message to Ebert where someone wondered why in vampire or Satan movies the priest was always Catholic or Orthodox. Well, if you are going up against Evil you want holy water and talismans and crosses and rosaries. You want real firepower. I'd like to see a vampire movie where the humans turn to the priest and discover with horror that he is just a Unitarian Universalist.