This feature is about the serif. That is the thingie at the ends of a letter. The serif keeps the T from falling over. The serif recirculates the essence of the s. The serif increases the vowelness of a,i, and u. O and e and in the word vowel, and need no further glory. Little i is so puny it gets a tittle on top.
Some say the serif is old fashioned, and will be sent packing in the future. Maybe this is the case. One typophile tells of Roman stonecarvers being guided by painted on letters. The end of the stroke was bigger than the beginning, so the carver made the bottom of the letters bigger.
A graphic designer, with the nickname Helvetica, told PG something about serifs. Studies show that serifs guide the eye through text, and make it easier to read. One gentleman reviewed studies, both pro and con, and decided that sans serif is just as readable as serif.