Why do so many people keep treating this as a moral decision by the NBA? It's a business decision with a moral pretext. No slippery slope is necessary - if someone threatens the financial well-being of the league by drawing the degree of negative response that Sterling's comments got, they'll be out too. "But what about this other thing somebody said 10 years ago?" Didn't get the attention, didn't threaten the business, so no response.
It just happens that racist, sexist, and, increasingly, homophobic statements are a very quick way of drawing that kind of negative response in today's market, far more so than in the past.