That works for a story with one or a few vampires, but on Buffy that would be way too much work for her to have to do with all the vampires around. You have to go with what makes your story work and Joss is pretty good about that.
Holy water, garlic, and Crosses only protect in Buffy too. I've never seen a Vamp killed with either on Buffy.
What about Blade. They go with Sliver tipped and made weapons to kill Vamps on that and that's totally different.