It's all in the tuning. The engine in the 2500 is probably tuned for a broader torque curve. Peak numbers don't mean much, its the power under the curve that matters. The 1500 may peak higher, but the 2500 probably makes more tq down low and through out the rpm range.
Where does the peak occur? My guess is its higher up in the RPM range on the 1500 hemi, which may not be as useable in a work truck. Also, the work truck is likely tuned for a fatter torque curve down low where it probably does most of its work. Advertised peak #s can be misleading.