Part of the reason it works well with restrictors is because of the fact that it produces great torque. When you have sanctioning bodies with competitive restrictions like Lemans or Nascar, the only option is to learn how to build a strong engine with as much torque as you can.

Take this for example:

Put the RSX - S engine and the Mustang engine in the same weight stock car with NA restrictions as per normal race specifications. For argument case lets say that the RSX engine (which actually makes 220 or so) was producing 260hp the same as the Mustang but only producing 180 or 200 lb/ft Which car would run the oval faster and why? Obviously the Mustang powered car because it is producing 300 lb/ft vs the 200 lbft of the RSx powered car. This is the reason that 4 cyl cars do not race 8 cyl cars and the reason that it is an advantage to have 8cyls because of the torque. In real race situations with strict rules and specs (other than losely guided weekend sports car club races......or street races without rules) the basic engine building fundementals of displacement, good flowing heads, good camshaft profiles, and good manifolds will always be the key to winning races, because torque is what you are after. Under restriced, real racing guidelines an engine making more torque than horsepower (or as close to it as possible) is very efficient.

EDIT: Even with forced induction for street cars, the torque problem doesn't suddenly dissapear or do supernatural things. Turbo raises performance but only enhances the base it is boosting. They now make turbo units for the 2003 Cobra and this months 5.0 mag has one features which is pumping out 737 horses BUT produces 719 ft/lbs of torque. Same scenerio except with technology that maybe is more familiar to most people on this board.