I have no idea why hybrids use the petrol engine when starting from a stop, but I was in one of the first few that came to Winnipeg as cabs (The first company to get them had the contract with the company I worked for. There's a law where if you work after midnight, the company hiring you has to pay for a cab ride home. Of course, that law went into the books when Winnipeg was the Murder Capital of Canada from my understanding...).
Anyhow, most of the cab drivers then had the diagnostics program up and running, mainly for folks like me, I think. And it stated which motor was working when, along with what was happening between the electric motors/generators and the battery. If I recall correctly, from what the diagnostics were showing (Which may or may not be accurate. It is just a basic "Here's what I'm doing" display after all), the petrol motor was attached to the transmission while the electric one wasn't.
This was, oh, six years ago, BTW. Most cabbies have the display on a road map now. Which is nice as well, as they're not constantly flipping to a road atlas book, due to the size of the Winnipeg Sprawl.
