It wasn't an upper-crust audience. Her staff had spent the whole summer going through the tons of letters they received to find people who really needed new cars. The people were brought to the show under a variety of guises - one man was told it was about teaching children in poor neighborhoods, a woman was brought to the show as a gues of someone who had "won" two tickets, etc.
Oprah Winfrey is a generous person with an extremely kind heart, from what I've seen and read. She lives the lifestyle of the rich and famous, but always finds time to give something back. From what I've heard, there are a number of charities in Chicago and elsewhere that truly owe their existence to her generosity.