It has all to do with some people being confused about things generally (uncertain in all scales), or else strongly feeling it is their natural right to be part of a dying breed. What usually surprises me is when someone comes from a summer holiday in Europe somewhere and says the temperature was a hundred or more. I realise that they must be speaking in Farenheit, but why did they go to the trouble of converting the temperature because there won't have been a Farenheit thermometer with hundreds/thousands of miles and all reports would have been in Celsius. Like you, I find this clinging onto confusing scales irritating (a bit like nearside/offside with cars - what's wrong with plain left and right, unless you simply want to confuse or pose with your own secret code). That is why I sometimes reply to the returning holidaymaker that, well, it was 292 (say, if it was 19 Celsius) here at home (Kelvin).