Well, Lizard King, your friend does not know what he is talking about. 97snakedriver has been the closest in his explanation about the difference of Japanese spec engines. It really depends on the car and the engine.
For example, the Japanese spec Silvia(240SX in the US and Canada) was available with a couple of engines that are more powerful than the truck derived KA24DE. These engines(CA18DET, SR20DET) are both factory turbo charged. The CA18DET is a 1.8 liter dohc turbo motor that makes 180hp in stock form. The SR20DET is a 2.0 liter dohc turbo motor that makes from 220 to 250hp in stock form, depending on year of the engine. This motor(sr20det) will also go into FWD sentras with slight modification(and of course a fwd tranny).
As far as the "280hp limit" goes, that is the max that the car can be rated although several cars(4th gen TT Supra, 3000GT VR4[called GTO in Japan], Skyline GTR's and V-spec, TT 300ZX, Lancer EVO, STi WRX, NSX Type S-Zero) make more than 280hp.
Any other questions about Japanese cars? I will be glad to answer.
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90 Honda CRX aka
Project Mongoose
Estimated Completion: 7/1/01
453 horses with a stock head...built head and LSD on the way
84 Toyota Supra
High flow cat, two chamber flowmaster, custom 2.5" piping, msd 8.5mm wires. Will have boost before 2002.
Have HKS turbo manifold for it
.....T04e next week