Sloppy Joe,
Let's think about that one for a moment. You point to the use of 5 A380s by EK, I presume, as evidence that CX should be doing the same. There are a few points to consider upon examining that logic...
Emirates' Dubai hub offers far more connection opportunities than does Hong Kong. Think about connecting to Middle Eastern cities, the Subcontinent, and Africa. Those passengers are not going to be buying tickets through HKG. Yet Emirates can still connect LHR passengers to all of CX's markets from Dubai. Think NZ, OZ, China, SE and NE Asia. It's a simple matter of geography. So it is not really a fair comparison, is it?
For CX, cargo matters, especially on the LHR route. With reduced European freighter frequencies these days, those 5 777s represent about 100-125T worth of daily cargo capacity (or about one 747's payload). If CX were to be running 5 A380s to LHR, there would be about half that much capacity (volumetric). Emirates is much less reliant on cargo revenues than is CX. Again, it is a simple matter of geography. The Chinese make stuff that folks in the UK want. The Arabs... not so much.
Also, there exists the issue of load factors and yields. If the company is to be believed - the problem in 2012 was cargo, premium passenger yield (not load factors), and high fuel prices. So, would an A380 (and its superior product) fix the yield issue? Are CX passengers going to pay more to sit in the A380 J seat as opposed to the 777 J seat? What would the A380 do to the load factors? Increase them because everyone wants to fly the A380 so much? I think not. The only thing an A380 does well is lower seat costs, but only if it is full.
I, for one, am glad pilots don't run our airline. We'd put CX right into a tailspin by bringing on massive capacity and flying it half full to all types of exotic locations. As geh065 pointed out, there are undoubtedly passengers out there that CX could be serving but doesn't. Those passengers go to other airlines when they fly, but their demand is very elastic. The yield they offer is usually low, and they go away when the economy turns sour. Let EK, Thai, and the like have them.