Wearing tennis shoes?

Is wearing tennis shoes with a suit or tuxedo a new trend? I've notice that a lot of the younger people are wearing tennis shoe with their suit or tux. Why spend so much money on a nice suit and pair it with a pair of tennis shoes? I'm 35, and I find wearing tennis shoes with formal clothing distasteful. Am I getting old and out of style? What are you thought of people wearing tennis shoes with formal wear.