I'm afraid that you've fallen into the trap of assuming that an aircraft can carry full fuel and a full load of pax. Unfortunately the vast majority can't!
To take your figures for the A380, the difference between MZFW and MTOW (ie the amount of fuel that can be carried with a full load in the cabin) is 446000 lbs which is approx 67575 US galls. if you factor this for the difference in range you end up with a figure of 109.5 US gall/pax.
The 747-400 figure comes out at roughly 116 US gall/pax.
I can't work out the figure for the A340 since you haven't qouted the MZFW.
regards
F40