Not completely true. Several high-output engines, such as those found in the Ford F6 Typhoon and mercedes Benz SL AMG luxury land-boats have a torque curve very similar to those that you get with the hp limiter.
The F6, for instance, would get to about 560Nm at 2,500rpm and just sit between 560 and 565Nm for the next few thousand rpm.
The Mercs do this:
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Yes, that's because they have electronic restrictors/limiters (it's all ECU work). Induction restrictor plates (this is what the description for the Power Limiters in GT5 states they are) or mechanical throttle limiters are unable shape power and torque curves in that controlled way and this is exactly the reason why they're used in motorsports in real life.