My thought process is that I bake on impulse and not very frequently so it's not worth having unsalted butter sitting around and potentially going off. I also can't be arsed to make a special trip to buy it because I would have gone off the idea of baking by the time I got home. Plus recipes almost always add salt, at least a pinch, sometimes half a teaspoon so it's not like the baked goods have to be salt-free. I'm not even sure if Kerrygold do an unsalted version, although I haven't really looked on the shelves.
Anyway, I don't think I can taste a difference, the only way to know for sure would be to make the same recipe with twice with the different butters. Nobody in my family has ever commented, they just eat it (except for the Guinness cake, nobody liked that very much).