where i went, they did not pay the same. engineering school was the most expensive, followed by architecture, journalism, business, and then finally "arts and sciences". the difference was only a few percent at each step, though. (IIRC.)
recall, though, that we're dealing with a market. the schools will charge what they can get away with for a liberal arts degree. if folks purchasing liberal arts degrees could do the math to realize they're getting a bad deal, they'd stop paying so much for them and the prices would drop. conveniently for universities, prospective psych majors don't spend a lot of time thinking about their expected lifetime earnings and how much their degree will change those earnings.
recall, though, that we're dealing with a market. the schools will charge what they can get away with for a liberal arts degree. if folks purchasing liberal arts degrees could do the math to realize they're getting a bad deal, they'd stop paying so much for them and the prices would drop. conveniently for universities, prospective psych majors don't spend a lot of time thinking about their expected lifetime earnings and how much their degree will change those earnings.