Ajo,
I would not be unusal to see posted HP/Tq numbers from the maker, and normally such numbers are always related to BHP (Brake HP or at the engine using a brake dyno). What we see at the wheel will be much lower and is what 99.9% of the sheets for dyno run would be showing. Also if you put it on a set of rollers with the wheel from mc turning, there is no true way to get the Engine HP-in case one tries to convince the customer they can do a direct conversion.
This is one of the reason that the maker will test the engine on a brake dyno to set their standards, for that is a pretty consistent factor, however what occurs with the many factors between the engine and the road varies too much to give a nice straight factor. Thus the roller or wheel dyno.
If I build engines, I will put the engine on the brake dyno and get a complete sheet for that engine, thus the customer knows that they have a consistent base to work everything else from. If one buys a crate engine say from GM and it is listed at 500 BHP, you can pretty much put the sucker on a engine dyno and get consistent run (within a very small +/- factor) even with a different motor (same build) as long as all the other parameters remain the same (oil, build, enviroment, intake, pipes, etc). but you put those engine in matching vehicle and you will get different HP and a much higher spread due to parasistic drags, and others.
Things like oil in tranny, primary, tension on chains, belts, clutch slippage, tire pressure, bearing drag, wheel mass, gear tolerence, etc.
Not that it really applies here, but I will give you an example. I used to race bicycles (at upper levels, including International). During that phase of my life, I was able to do some intense testing and measurements, one thing that made a difference was the type of bearings we would use for the wheels and bottom bracket, as well as the rolling masses of everything from the wheel to the crank and bottom bracket.
Most would not think much of this, unless you peddle such over a few hundred miles for a few days. In that case what little difference between a steel crank axle compared to a Titanium would or between even down to if you used a ABEC 5 Bearing verse a ABEC 8 or 9 would be a factor and too many worth the higher cost. The same would be for the tires and one of the major reason that many use true tubular tires to much higher pressure (I would typically run tubular with 160 PSI in them for racing)
In my case allot of stupid money on nothing but Campagnolo Groupo that did not make me any better per say, but left any questions out on my componets. People think motorcycles can eat up some money, get into serious bicycle road racing and you will really be shocked considering it is a bicycle.