I wonder if that is because Ford phased out the Econolines, so parts and tires are harder to find.
From what I know in my neck of the woods, Ford upfits may or may not be servicable, but because Sportsmobile is in the area, there are at least 1-2 "blessed" dealers which can service those. There are some "B"s sold, so both the MB and FL places have at least seen a "B" or two. Chevy places see conversion vans all the time. Which gets me wondering how the Dodge/RAM places will deal with upfitted PMs.
If I wanted the best dealer network for the van chassis, I'd go with Ford. For dealers which are versed with "B"s made in the past few years, I'd probably have to give the nod to the MB dealers.