I admit I know virtually nothing about the aircraft industry, but I always wonder why Airbus doesn't do the initially planned cargo version of the A380. The only reason I can imagine is that there aren't enough customers for the cargo version, but why is this so? Isn't air cargo growing? Would an cargo A380 be too expensive? Some comments suggest the A380 has bad fuel efficiency per passenger mile, but some others suggest this is because airlines put less passenger seats in the plane than possible. Surely this can't be a problem for freight planes? What is it?