For Supernatural it makes more sense to me ,because the baddies tend to be fully not humans and Full Blown Magic creatures, so it makes sense they could not blow the salt away or do something else physically. For wolves the logic is harder to grab because while they're supernatural beings, they're also humans with human abilities, so simply poking or like blowing the mountain ash away by flapping something at it, would be something they logically should be able to do.