Such a taper is a necessary consequence of having a limited power source. Well, maybe not completely necessary. An alternate solution would be to restrict the torque and RPM to lower values. But that would not be an improvement.
Does the electric motor have 300 something foot pounds of torque capability? I thought I read that some where a while back? Mike
"The electric motor on the Prius [Gen II] is rated at 67 horsepower from 1,200 to 1,540 rpm. It produces 295 pound-feet of torque from 0 to 1,200 rpm" from: HowStuffWorks "The Toyota Prius" Read the whole thing. There is no limit on the torque below that, other than traction control.