I have noticed the same thing. I can't play defense at all on Veteran, but it seems like I can on All-Star and Hall of Fame. On Veteran, it really seems like the AI never misses a shot, especially against the better teams. I started thinking that maybe it was "compensation" for their weaker defense, and I think that might be right. It is so easy to score on Veteran that you would be winning every game by 50 if the AI didn't hit every shot.
I have found much better playing games on the higher difficulty levels. It isn't because the game is too easy, either - there is just too much "cheese" and "that shot should have had NO chance to go in." On the higher levels, they don't go in.
The ball distribution is also better on the higher levels. I played the Thunder on Veteran (with the Suns), and was completely lit-up by Durant and Westbrook, but by absolutely NOBODY else. Jeff Green had 2 points and nobody else scored. I moved it up to Hall of Fame, and all of a suddenly everybody is scoring (even though Durant is a beast and gets his points anyway!).