That was my thoughts.
Also for short trips in congested areas where alot of starting and stopping occurs and the system has a chance to use it regenerative braking etc, Hybrids work well, but once on open road, the benefits of a Hybrid aren't really realised. So if a Taxi driver is doing hwy runs from City to Airport all day, he may as well be driving a full petrol powered car.
In the recent solar challenge held in NT, which also has a production car class, the New Hyundai i30 Diesel and the Peogeot diesels completely flogged the Prius in fuel consumption. Although diesel emits more pollutents per litre consumer, its greater efficiency means less actual pollutents are emitted in the end.
I can see them being of benefit in some place like New York, but, again space is a concern.
Ideally, I would commission a car maker to build a spacious people mover type vehicle (No bigger than say an Avensis Verso), that is bare as bones basic and light weight, cheap, and run a hybrid/lpg drive train developed specifically for the task, it doesn't have to have big performance figures because it only needs to get to no more than 100km/h