Yes the maximum is for the lightest truck possible. So, a S model with zero options. Every option you add from there subtracts from the payload. Long bed will be a hit, SV trim will be another hit, additional packages another hit. In the end you lose significant payload as you already noticed. I think the true maximum actually starts off much higher than 1,160 lbs.
My truck is a short bed crew cab 4x4 SV with tech package and convenience package, so pretty well loaded up. My sticker shows 1,160 lbs.
I've seen Chevy Colorado ZR2s and Toyota Tacoma TRDs that have only 950ish lbs. of payload remaining on the sticker after all the off-road goodies are added! That's pathetic!!