You haven't had a proper cup of tea probably. ;)
Different teas require different water temperatures AND different steeping times for the best taste. Generally the less oxidized the tea the lower the water temperature. I find the worst offense is most Americans over steep their tea which makes it very bitter!
People who use a thermometer are very serious. I just guesstimate.
Also, get some high quality tea, the difference in taste is amazing and its not that expensive, only a few cents a cup.
Also - you can reuse tea leaves.