We have tons of ulgy orange Prius Taxis in sunny Singapore too. http://www.asiaone.com/A1MEDIA/motoring/20091109.113554_prime_taxi.jpg
Someone needs to tell them that it's ok to shut off and restart because you won't wear out the "alternator" (which is my guess as to why they typically idle). Besides, most cabs never get shut off so they're warm 24/7 which means even with their aggressive driving, they could be getting better mileage than some owners.
If the gasoline engine is running while the Prius is stopped, I assume that this is mostly because the cab driver has the cabin heat turned on, which would be a reasonable wintertime practice...
Spartan Cab Company, here in Lansing Michigan use the Prius for their cars. Also, whenever I visit Chicago, the red prius is a very popular Taxi....you see them all over the city.