I understand the reasoning, but are recipes written with the assumption that people will be using unsalted butter?
What I mean is.... it's easy to add salt to a lot of dishes later on, based on personal preference. Unless I'm making a specific type of salted toffee/candy, though, it's unlikely I'm going to salt a baked good after it's done. I can't imagine salting my chocolate chip cookies, ya know? And I'm not going to be able to taste the difference in the raw cookie dough usually.