Those extra 120 odd pax get VERY expensive.!
But how many more W/J/P pax can a 380 take over a 777? Id say a seat on a 380 is probably worth more than a seat on a 777 on the same sector.
I still think theres a gap in the fleet somewhere between a 330 and a 380 that a 777 should fill though. If you could replace all of the 747s with them tomorrow or even three years ago that is.