This is simply a matter of being used to one system. 105 degrees Fahrenheit means nothing to me but I know right away when I see 40 degrees Celsius on a thermometer that it's really, really hot. Fahrenheit is obviously more precise since the increment in heat is smaller for each number, but that's what decimals are for. All my thermometers measure and display at least tenths of degrees. Oh, and all scientists use Kelvin. It's the only system that makes any real sense for measuring what heat actually is.
About the date system - the way you say it is a byproduct of the way you write it. I write it 'the 21st of December', and I say it the same way.