It's no one's fault except those who drive in an unsafe manner in bad weather.
I both agree with Cam Woolley, with a caveat: even if weather takes you by surprise (which can happen) as a human being you should not only be clever enough to adapt by slowing down but also have a more finely honed sense of self-preservation.
Now, have we seen any charges against anyone from the accident on the 400? The police certainly have the discretionary powers to charge anyone involved with dangerous driving, following too close, speeding, etc. Proving that charge in court may be another matter.
I recall one snowstorm that closed several highways. Luckily, I was headed in an opposite direction but stopped to get gas and was hailed by a guy who wanted directions. He'd come across a police roadblock and was wondering if there was some 'back road' that could get him where he wanted to go.
I told him that if the police closed the highway the concessions and sideroads wouldn't likely be in any better shape. Exasperated, he wondered aloud how he was going to reach his destination. "Obviously," I replied, "you aren't. That's what happens when the police close the highways."
I had a good laugh at this guy's expense but his mindset is aggravating. Why put yourself and the cops, EMS, firefighters and plow operators at risk when you roll your car on a closed highway...just because you won't wait a day to get to your ski chalet?
But I digress.