They don't need to bend the laws of physics. And the raptors 100 lb wheels aren't like they're 50 lbs heavier than any wheels before. Rubber is lighter than metal, earlier trucks with 20" or 22" wheels weigh just as much if not more. My 00 HD truck wheel/tire combo weighs 95 lbs a pop.
There's still a good amount of stuff Ford can do to improve mileage on trucks. And the 6.2 is an outdated dinosaur before it even hit the trucks, just look at the differences where it lags behind the other drivetrain lineup that are touting improved performance and improved fuel economy over previous year drivetrains (3.7 V6, 3.5 TT V6, 5.0 V8). Aluminum blocks, 4v heads, electric power steering, direct injection.
I strongly believe the 6.2's days are limited. I bet within a few years it'll share the base powerplant with the 2013 Shelby with a 5.8L aluminum block 4v V8, just as the N/A varient while the Shelby is the s/c varient. And it'll probably make more hp as N/A than the 6.2, and better mileage.
