Yeah, but did Buffy and Co. use magic to kill Adam because that was the only weapon they HAD? If they'd have had a bone dagger like the one that killed the Beast, but for use against Adam, wouldn't they have used that instead? You can't compare those deaths like that, I don't think....it's apples and oranges. Each baddie had their intrinsic weaknesses. The Beast's was the bone dagger, Adam's was his power core that Buffy pulled out with magic.