Nosferatu was a loving creepy movie.
Authors change up lore for money. It's always been so, so it'll always be. The vampires that we saw whispered about in hushed tones over a pint of ale in a gloomy Transylvanian tavern four hundred years ago have been so satirized and parodied today (particularly in kid-friendly Halloween TV movies) that no teen girl would buy a book about it. If an author wants to market to the teen girl these days, the vampire needs to be powerful, enigmatic, and above all, forgetable .
So we remove the tendency to turn to ash in the sunlight. That's not exactly convenient if our vampire is to attend a high school. Girls like sparkles, right? Let's make him sparkle in the sun so he can be all whiny about "THE SKIN OF A KILLER". And we remove the aversion to garlic. How is he to take his human girl on a date to some fine Italian restaurant if he can't handle a little garlic? We remove the aversion to Christian symbolism. We'd get burned down by angry mobs for that. And how is he to spy on his human at night if he can't enter without being first invited? Let's remove that tidbit too, it's not like anyone would notice. And the blood thing? We can make him drink animal blood so he's less horrifying. And for forget's sake, let's make him a teenager.
We now have a mysterious, tragic, piss-weak little bitch that we dare to call a vampire. But at the very least, he'll make us a forgetton of money. And while we're at it let's throw in some werewolves. Only they can transform at will and don't have anything to do with the full moon. Or gypsies. And let's make them loving ripped .
In the end, it all boils down (like a vampire in the sun, dohoho) to making monies. Although, I suppose I seem to be saying that you can only market to teen girls if you're writing of vampires. I've noticed that when marketing to other audiences, vampires change little. Your Being Human vampires even burn up when they enter a house uninvited, for example. It seems that authors change vampires to fit their genre, and to be unique and creative, and to appeal to their target audience. It's just the way it is.
