Why the ampersand survives
The ampersand began as a ligature of the Latin et. Look closely at an italic cut and the two letters are still there, joined at the crossbar after nearly two thousand years of handwriting and type.
Measure, and the comfortable line
Most readers settle best at somewhere between forty-five and seventy-five characters per line. Beyond that, the eye struggles to find the start of the next line; below it, the rhythm of reading keeps breaking.
Old-style numerals in running text
Lining figures stand at capital height and shout a little inside a paragraph. Old-style figures rise and fall like lowercase letters, which is why they sit so quietly among words.