52049er:
You're right for the difference in technology but it would be fair to mention that 747 is a 60's technology a/c while Airbus (any model) came a generation later.
If you do a comparison with 777 it would be a different story. Same holds for 37NG and partially for 67s and 57s.
I've been working both sides and to tell you the truth it is more or less the same, in the end. Amount of work in MRO is what it counts and systems and engines are far more complex and demanding then structure.
Cheers