Bread-Bakers v103.n053.12

In one phrase: Salted butter generally means old butter. Butter past its 
prime is generally recycled by salting it to mask off flavors and to 
further extend its shelf life.

In bread recipes, using salted butter will not alter the chemistry of the 
recipe by that much (although it may alter the taste of the bread). But in 
cake and pastry recipes, where a delicate balance must be maintained, it 
certainly does.

Roxanne