A significant percentage is availability, with the rest going to warranty.

Retailers with QUALITY biofuel are pretty few and far between. In the Dallas/Fort Worth area, the biofuel retailers are in either downtown Dallas, or downtown Fort Worth; it's a 60-mile round trip to get biofuel for me (of ANY kind, much less quality) when non-biofuel is 4 blocks away -- and one of the cheaper stations in the area, to boot. (As a matter of record, if I were in Austin, I'd buy it a lot more; there, you're never more than 5 miles from a bio-retailer, usually B20.)

Running anything but QUALITY fuel in a 6.0 hits a little too close to home on an already skittish warranty policy from Ford. Ford endorses no more than B5, and that concentration is too low for it to be worth the effort for most retailers.

As the 6.0 platform ages a little more (i.e. running out of warranty), you'll see more people using it.

Part of the problem, too, is that there are still too many people who equate "biodiesel" to running old french-fry oil. This is what kills it for a lot of folks, Ford Corporate included. There *IS* a difference between WVO and commercially-prepared, properly blended, and taxed, biodiesel, and THAT's a perception problem that'll take a LONG time to fix.

-blaine