I don't think the incentives are really any different. The reward for making it to the NBA was unimaginably large for most young kids then, and it's still unimaginably large. I don't disagree that the average athlete might be a little bit better, but I strongly disagree with the "much better" statement. I think that most of the stars of the 80's would be very relevant, and likely stars, in today's NBA.
When I think of the 80's I think of Magic, Malone (Moses and Karl), Erving, Jabar, Bird, Jordan, Thomas, Stockton, Wilkins, Hakeem...
Players today aren't "much better" than any of these guys.