AFAIK cost of shipping via USPS varies by location zone, i.e. the bigger the distance, the bigger the cost. Not sure if Fedex and UPS have similar rules.
Well, so why don’t retailers who ship by USPS adjust shipping price based on customer’s zipcode? I do understand that they often embed extra fees into shipping and so forth to raise the price, but still, why don’t they just add those fees as markup on top of the accurate shipping cost via USPS, hence avoiding subsidizing the faraway customers at expense of the nearby ones?