Guess what, Canada sets the freezer at -15 Celsius. The USDA just chose 0F because it's good enough and a nice easy to remember number, there is nothing special about it.
Same with all your other numbers, your just using whatever the closest even F value is that's easy to remember there's nothing special about any of them and we have equivalents in Celsius
There wasn't much of a real "threat", in that planes wouldn't fall out of the sky. but banking systems would probably get quite confused, and potentially lead to people being unable to access money easily until it got fixed.