One of the biggest changes for SAE gross to SAE net was the engine has to be fitted out with all accessories it would have on the car. Also when the manufacturers do the certified,published testing an independent SAE engineer must be present during any and all testing to eliminate any "funny business."
SAE net horsepower
The brake power (power available at the flywheel or output shaft -- usually the crankshaft) of a
fully equipped engine fitted with all the accessories necessary to perform its intended functions unaided. In 1973, automobile manufacturers began publishing their engine specifications in net horsepower and net torque instead of gross figures. In many cases the published numbers were significantly lower in 1973 than in 1972. Some of the decrease was attributed to the addition of pollution equipment, the lowering of compression, and the use of regular unleaded gasoline instead of premium leaded fuel. However most of the decrease in number was a switch to net figures.
http://www.motorera.com/dictionary/sa.htm
Also consider that you can gain a few HP (~15) just by utilizing underdrive pulleys, so eliminating the accessory all together (if they could) would gain even more. I would think that the power steering pump would be a bigger loss than the increased load of an electric PS pump on the alternator, probably why they go to those.