VSC that is "available" for the 2009 Prius... In other words, the car doesn't really come with it. The original comment doesn't seem to indicate anything about VSC. Might be a defective car.
I work for Hertz. We have had Prius's since 06. This car shutting off in snow and slush is nothing but a dream...
I am in Montreal too, so plenty of snow and slush and ice over the years. I have noticed in Montreal, when you are trying to get out of snow, there is no T/C shutoff, which would allow me to spin the wheels (this is on all versions I have driven, including the one with the smart key and JBL system), but the engine didn't shut off.
As a previous owner of two VW TDI's, both of which left me crawling on the side of the road with black smoke coming out the back and unable to exceed 10 km/h, I would gladly have a Prius. I live in the country though, and I now have a Volvo XC70, which I will buy another one when this one goes (it now has 378k BTW).. Want a TDI? All yours!
I believe what you're experiencing, is while driving aggressively, you encounter road deformations or slippery conditions, and the car kind of "holds you back", unlike in other cars. I noticed this in my 2009 Prius while driving in the rain and trying to pass an unsafe driver. It was unexpected, but did not cause me to lose control. I simply backed off the accelerator until I had regained my grip. The ASV takes some getting used to, but I find the Prius a competent/safe driving vehicle, but as any professional driver will tell you, "know your vehicle's performance capabilities - and do not out-drive your car!".