From what I understand, in order to fit the bags in the desired configuration the 180 rear tire was a necessity. The H rated tire is only rated for 130 MPH. That, coupled with the slightly higher torque needed for two up, fully loaded, passing situations resulted in the lowering of the horsepower rating.
I doubt Triumph really considered our propensity for 'heavy underpowered touring bikes'. If they had, they could have just put the package on one of their twins. In case you hadn't noticed we also seem to purchase high powered sport bikes in fairly large numbers. We're not all fat cruiser riders, regardless of what you may see on TV.