Ken,
One C-17 needs 4 C-130 loads to fill it up, which isn't always that convenient. One C-17 can only be in one place at a time, while 4 C-130 can be in....
Same arguments for the A400.
Isn't the French deal all basically about tanking, which the A400 hasn't managed for them? They can buy Herks and have an instant tanker with all the clearances and experience and no mucking around.