I don't understand why the 4.10 and 4.30 gears are the only ratios available with the V-10 in trucks, either. The Excursion, I think, came with a 3.73 rearend. Historically, the Excursions get better fuel economy across the board with any engines than it's F-250 counterpart. I'm sure there is no weight difference worth nothing, either. My wife and I had a 2003 V-10 Excursion and could pull just over 16mpg on our highway trips down to Pigeon Forge every year with a fully loaded vehicle, air conditioning on, and cruise set at 72mph. This wasn't a one time trip, either. Now, winter driving around town, well... about 10-11mpg.
I can understand that some say the different size wheels and rubber (larger) on the trucks with the 4.10 are about as effective as the 3.73 gearing, but the mpg numbers don't prove that. I see ford offers the SFE package on the 2009 F-150, so why can't they offer something similar on the other Superduty drivelines? If you order the smoker's package, you know your going to smoke and the interior of your truck will smell like an ashtray. So, if you order the 3.73 gears with the V-10, your highway mileage will go up, but your towing capabilities will drop and your truck may be a dog out of the hole. Okay. Remember the old days when you could order a "highway axle" on a car? My old 1976 Cutlass had a highway axle. It was a bear to get moving, but once you hit highway speeds, it was unstoppable. My old roommate from college found out the hard way his Berlinetta wasn't a match to my Olds cruising down Highway 51.