R1100S - Flywheel?

[ariadirect]

I recently rode a friend's '04 R11S (mine is a '99 model) and the motor seemed to spin up faster - which is to say, it was quicker to rev. I've also put some time on an '07 R1200GS which is definitely revier than my motor. Question: Does anyone know of any alterations BMW has made to later model flywheels? Are they lighter? Can this be applied to a '99 model bike? And if the flywheel isn't the culprit, what is?

Thanks for your input.
AR