“Freezing temperatures” mean “freezing temperatures,” though, and numbers are pretty irrelevant. American schoolkids learn that it’s around 32°F and 0°C, and we easily remember it, but the weather forecasters still say “frost warning,” or “freezing rain,” rather than “it’s going to be 32°F tomorrow,” because there are so many confounding variables. Even the temperature of the phase transition is kind of squishy, since pure water freezes at 0°C at STP (except when it gets super-cooled). And if we’re talking about the fundamental importance of water, then I might argue that 4°C is the important temperature, because it’s temperature at which water reaches its maximum density.

Anyway, not to say that Fahrenheit is great, or anything, just that Celsius is similarly arbitrary, and we lack a compelling reason to switch. (Even though virtually every thermometer I’ve ever seen in the U.S. has both scales on it.)