The answer is that it depends what side of the Atlantic you are on. In the British Isles, sport commentators, sportscasters, presenters and pundits almost exclusively sit (when on screen), and till/checkout clerks in food shops almost always sit while on the job. In the U.S., both stand on the job fairly exclusively.
Another UFOD: The most popular form of sport commentary is a duo, almost always consisting of a professional journalist/broadcaster and a former professional in the particular sport in question. Two exceptions to this occur in the U.K., where all current snooker and cricket commentators are former professionals of their respective sport.