The rear brake is for making flat spots in the rear tire!
I bought my race bike from a guy who is shorter than me and has quite a bit shorter legs, but he had the levers rotated way down from where I like them. It is just a personal preference and personal geometry issue, not a matter of how tall you are. One of the reasons I bought the bike I did was because its previous owner is the exact same weight as me, even though he is a few inches shorter.