I bet it has to do with block heaters. No block heaters, busses are a pain to start. No starting school busses, no picking up kids. Minnesota would likely have block heaters, Ohio wouldn't. My family is from Thunder Bay, Ontario, so I'm familiar with low temp procedures. Never, ever closed a school for cold weather in my memory.
In my 13 years of public school in Nova Scotia, school was closed because of extreme cold once, when the high for the day, including wind chill, was -50°. Now, of course, out on the prairies, or in northern Quebec or Ontario temperatures close to that without the windchill are not so unusual, but then people who live there are equipped for and used to dealing with it. In NS -20° was an extreme cold snap.
Schools were regularly closed for snow, however, where I lived out in Halifax County - maybe 2 to 4 times a winter. Most kids were bussed to most schools and I guess they didn't want to take the chance of running the busses in bad conditions.
My next door neighbor has a block heater on his diesel truck. All the houses on my street have an electrical socket between the garage doors to make the practice of using a block heater easy. I don't have a block heater on my F150 4x4. I've had no problem starting it all winter...even on days when in was -9 F. It does take a few extra minutes to scrape the ice off the windshield and warm the engine up sufficiently to keep the windshield clear with the defroster. I have to drop my son off at work by 8:00 AM. We leave at 7:40 AM (before sunrise). That is typically the coldest point in the day. We had 2 weeks of morning between zero and -13.
It warmed to +48 F yesterday. The snow has been melting off the roof. It has been there since mid December.