If you were to only account for 747s that were bought for their size then the 747 program would have been a giant flop that bankrupted boeing.
What people forget is the 747 was revolutionary not really for its size but its RANGE! By Boeing's own admission long before the A380 was even thought of, two thirds of all 747s were bought for their range, not their capacity. Now that there are aircraft like the 777 and the 340 that can do the same range with less people and make money, the demand for 747s has dropped off. The 777 was originally thought to be a medium range airliner, but the customers kept demanding more range. Boeing complied and increased the range of the 777, but they weren't happy about it, they knew they were killing the 747 in the process.
With Airlines now free to buy any number of aircraft with range that is for all practical purposes 1/2 the circumfrence of the earth, the demand for the A380 will be stictly based on traffic. With the continue fragmentation of routes with more point to point flying (Open skies coming to Europe and USA will be another example of this btw) requirements for larger aircraft will drop.
Will Airbus sell em? Of course they will. Will they sell them in greater numbers than the A300/310 (which lost money because they only sold a few hundred of them) not likely. But Airbus doesn't have to take financial considerations into effect when they launch a product.
When Boeing launches an aircraft they have to borrow the money at market rates to do the research, set up the line etc. Airbus got a ****pot of grants that made this part of the problem tough. Lets say Airbus sells 500 of em in 20 years (A VERY optomistic assessment) each aircraft already costs 60 million dollars before you clock in the first worker and cut the first piece of aluminum (principal+interest assuming around 5 percent interest) If you don't sell that many aircraft that quickly and deliver them, the interest compounds and things get REALLY out of control. OF course not having to make those calculations are a wonderful advantage airbus has...
Cheers
Wino