It's worthwhile pointing out that there have been significant changes to aviation since, most notably the move to twin-engine aircraft. But ultimately that was

It's worthwhile pointing out that there have been significant changes to aviation since, most notably the move to twin-engine aircraft. But ultimately that was made possible through small incremental improvements in engine design (and material sciences and manufacturing). There haven't been similar leaps forward since. The Boeing 747-8 is 29% more fuel efficient than the 747-100 in absolute terms before you even start considering the extra space it has as a larger aircraft. Some of that is aerodynamic refinement (and they're limited by starting with the older airframe!) and some of that is newer engines. And the 747-8 is relatively poor compared with many newer airframe designs.