Wilson and the NBA claim that the ball is exactly the same as they have always been and they do not indicate what the difference is, or why they changed it. I think that for someone like you and I we wouldn't even notice a difference at all and it's tough to say if there is a difference or if the players are just using this as an excuse.
I think it is just an excuse but the players who are complaining that it doesn't have the same "feel" and "softness" of the Spalding balls that have been used since 1983.