The wormholes are from the non-Asimov prequels. In the first one, by Gregory Benford, it's pretty clearly intended to be an update and a retcon; there is no hyperspace, just wormholes, and that's how it's always been. The second one by Greg Bear explains why there's no wormholes in the later books-- that doesn't really explain why they weren't in earlier ones! But throughout he was pretty clearly working his best to smooth out some of Benford's weird ideas.
Well, I wouldn't know about that since I've never read any non-Asimov prequels.