My theory is that hybrid vehicles are programmed to offer a slow startup to give you a chance to reconsider if you really want to accelerate at an unnecessary rate of acceleration. I have noticed this in my wife's HCHII and also in our work "truck" the FEH-II (2008). This could be contributed to the CVT also, with programming to limit the torque going in. The only hybrid I have driven that does not display this behavior is my HAH. When I floor it the only thing that interferes is the traction control because without it, the tires would be reduced to a pile of ash.