I believe Spielberg doesn't need Potter credit to be one of the greats in cinema. I've heard a few years ago that he was somehow linked to the 1st film, which for me is one of the best. Maybe he didn't said anything before because the movies were still being made...

Actually I believe he made the best option and I'm happy that he dropped it. Animated version wouldn't work well on HP (imo). And we wouldn't have Alan Rickman as Snape