1. VHS didn't have any special features, deleted scenes, trailers, etc for the most part. These are standard and common now. Filmmakers have started finishing scenes that before DVD would never have gotten filmed just to include them on the DVD. People love special features. HD-DVD/blu-ray and DVD both have them. So that won't be the motivator that it once was.
2. Draconian DRM on the HD formats. That is its own can of worms that I won't get into here.