My first post, but I got all excited when I saw that I though I knew something.
I believe the reason for the short barrels is that the larger calibers like 45 Colt, 475 and 500 Linebaugh do better from shorter barrels than do smaller calibers like the .44 mag. Larger diameter, heavier bullets just don't require the long tube to get the most useful velocity range. If you look at tests of the new S&W 500, there really isn't that much velocity loss from the 8 3/8" Bbl to the 4". One would expect a greater difference. Also, Hamilton Bowen and John Linebaugh believe in the most power from a portable package, as they feel long barrels are not as useful in the field from a portability standpoint,especially given that there is not all that much to be gained velocity wise. And you can learn to shoot the shorter barrels just as accurately as longer ones. Big bullets, not big guns.