You could fly a B757 across the Atlantic with as few seats as you liked, and still make a profit-it all depends on how much you charge for each seat-BA charge extraordinarily high prices in Club or First Class-which is why seat numbers overall are quite low.
BTW, my father flew LHR-MAD rtn with BA in Club Europe class last month. Ticket cost=750+ pounds!!
Fortunately, his Company was paying.