thats because thats not where it gets most of its E from.
Regenerative Braking is where it gets most of its E from. otherwise there would be little benefit to running a hybrid. :-) ie everytime they stop they recover some of that energy (a lot actually its really impressive) which reduces the demand when they GO again.
also the IC's are instant on. they are shut off when at a standstill when you GO if there is enough E you just go on electric and then at around 25mph the IC kicks in to provide the extra go power. when you "coast" or brake to a stop the IC turns off and the regenerative braking kicks in so your now not using any gas and your recovering E from the regen system.
Pretty cool the problem is 50mpg blows. a 25 year old rabbit gets that and any modern vw or mb diesel can also get that.
Just wait till they can make a diesel instant on (they are working on it) then you will see some truly impressive mileage. if they do not intentionally cripple it. 150mpg should be easy with diesel and new battery tech.
Chris Taylor
http://www.nerys.com/