Actually, accelerating and braking hard with hybrids is *good*. It's been demonstrated that gentle acceleration is worse for overall mileage than accelerating hard and then maintaining the fixed speed. And braking is regenerative anyway, although admittedly hard braking also uses regular brakes, whereas gentle braking would mostly be regenerative.

But as someone who grew up in New York, I can tell you taxis, like everyone else, spend most of their time stationary. Hybrids were designed for city environments and it's just dumb for taxi companies not to buy them. They'll save themselves so much money.