I still think field-weakening has something to do with this, as I noted in;viewtopic.php?f=31&t=13767
Tesla has an induction motor. Renault (Fluence/Zoe) use a coil rotor. Volt has a gear set system that could, in theory, shift the motor's performance so it keeps its perm mag motor to its design for V/Hz.
Leaf flies out of its V/Hz range from some >35 mph, so I am lead to believe from its torque figures.
Tesla and Fluence have a Cd of ~0.25. Volt and Leaf are ~0.29. Real aerodynamics is not as linear as a bald Cd figure might lead you to believe (SCx for all are around the 0.66 m^2 figure), but the lower Cd should mean relatively lower impact from high-speed effects. Leaf might seem to suffer from relatively high aerodynamics, combined with the adverse effects of field weakening above its constant V/Hz range.