That's a distinction I made early on. The Power Wagon very likely has additional payload to be gained by adjusting the suspension because the underlying platform is mostly the same as what's used for the 2500/3500's with higher GVWR's. Now I'm not necessarily saying its wise to exceed the OEM's recommended payload for the PW.
The same argument can't be made for the Tacoma; there is no factory-produced variant of the Tacoma with a higher payload. The GVWR is what it is.
Edit: By the way, the 3500 dually has a different axle from the SRW 2500/3500.
Same axle, different ring gear diameter. Literally the actual ring and pinion and the diff cover are the only differences. Actually, if you convert your 11.5" axle to a 4.30 ratio it automatically becomes an 11.8 because that the only size that ratio comes in. The only thing you have to change is the diff cover.