Could be that the factory 1700 adheres to EPA regs better than the BB. I don't know. I'd like to get the definitive answer but i doubt we ever will. I figure two sources tho....why would 2 different sources just come up with this same idea ? So i'm leaning towards the likelihood it's true.
Just so happens I had a discussion with the service manager at my dealership last month about how Triumph produces their machines for the world market. Apparently the EPA comes in a distant second to some of the European countries regarding air pollution AND noise abatement. Our bikes leave the factory ready to be sold anywhere in the world. He told me that's why easier breathing (intake/exhaust with a tune) provides such a boost in performance.
Look what the Short TORS and fixing the seal on the air filter did for you. The Storm suffers from being built to meet the most restrictive standards. It makes sense that the BB cams would provide the best improvement in power. They were developed apart from a complete engine that has to meet emissions limitations. After all the factory is not held responsible if a rider/owner installs off road parts on their bikes and uses the machine on the street anyway.
It's funny that HD charges extra to buy a bike set up for the stricter state emissions standards rather than building all of their machines to meet them. I for one am glad to see them think that way. I'm tired of the many suffering for the whims of the few. The Soap Box has been vacated.