You gotta remember that is power at the crank. Deduct about 20% for an auto and 15% for a manual and then you have close to the power at the wheels it has
Like the gmc typhoons were rated at 350hp cause GM didn't have a tranny that could handle the higher output of the turbo motor was putting out. It was a way to not warranty the tranny if any mods were made to make more power. Even for something as simple as a retune
Just like mph ratings are measured by going 55 mph