For me, some of the quantification desire comes from changing conditions. Unlike so many other activities, skiing is considerably different every day, even if you ski in the exact same place. I suppose this is more diary-based rather than pure quantification (I don't really care about total ski days, as I know each day varies so much), but skiing simply invokes within me a desire to permanently record my experiences. I couldn't care less how many times I play tennis during the summer, but I definitely want to know how many powder days I have each winter.