Typically BA 777 and 747's are configured with the same number of First & Club Class seats. As the 777 is smaller this means reduced numbers of World Traveller seats.
Seeing as BA's always going on about increasing 'Yield' they rake in pretty much more per 777 as for the 747. When you take out the operating costs etc, the "profit" is more.
Hippo. (If pigs can't fly then neither can I)