Thats not quite true but the theory is sound.
On the Dodge diesels a 4.10 axle ratio will give a higher rating than one with 3.73s. However the drivetrain, including the rear axles and brakes is exactly the same between a 2500 and a SRW 3500. The only difference between the two trucks is the rear leaf spring pack and the decal on the door. Add a set of airbags to a 2500 and you now have the same capacity as a SRW 3500.
There are also two different numbers to look at for towing capacity, this applies mainly to the heavy stuff, not so much SUVs.
GVWR-gross vehicle weight rating, how much the truck can carry. This is the max amount the truck can weigh with people/fuel, cargo in the box and hitch weight. Trailer weight does not come into play other than what the hitch weigh adds to the trucks weight. Subtract the vehicle's curb weight from the GVWR and this is roughly how much the truck can carry. This is where a DRW(dually) has the advantage as its dual rear wheels allows for a much higher weight carrying capacity.
GCWR- gross combined weight rating. This has to do with how heavy a trailer you can tow. A Dodge 3500,SRW or DRW have a GCWR of 23,000#, so the truck, all its gear, cargo, fuel,people and trailer together must weigh less than 23,000#. So take the weight of the truck, cargo in box, people,fuel etc, subtract that from the GCWR and that leaves how heavy of a trailer you can tow. Here's the interesting thing, because a DRW truck weighs more than a SRW truck the SRW has more left over for the trailer. Technically a SRW truck can haul a bigger trailer than a DRW. Same goes for 2wd/4wd, a 2wd regular cab truck will weigh less than a 4wd crew cab leaving more left over for the trailer.
Realistically though a trailer THAT heavy is going to require either a 5th wheel hitch or gooseneck hitch and will transfer so much hitch weight to the truck that you would exceed a SRW truck's GVWR or overload the rear axle rating meaning that a trailer that big/heavy would require a DRW to handle the hitch weight.
Here is an excellent site for figuring out the tow ratings on almost any 2002+ Dodge vehicle. Sorry no Jeeps in it.
http://www.dodge.com/towing/D/vehicle_to_weight.jsp