John's likes sneakers that are good for playing tennis, even though he doesn't play tennis nowadays. His favorites are a pair of well-broken in, old sneakers that are easy to put on or take off.
Em's won't wear puffy, over-fancy sneakers, or one's that are emblazoned with the name of the manufacturer. John isn't interested in sneaker styes, just convenience and comfort.
That sneakers have evolved from inexpensive deck shoes, to fancy, expensive ones, named after famous athletes, relates to the way the Cullums themselves have evolved.