I don't think this is going to effect sales of Blu-ray to anyone but the enthusiast market. Most lay people just aren't going to give two shits about being able to play along with the movie. The enthusiasts will just hold off until a "proper" release is available.

The studios can try to double dip with these interactive features all day long. Their core market though, people who just want to watch movies, aren't going to take the bait. They'll probably rebuy all their HD-DVD titles on Blu-ray when they're released, but they're not going to worry about making sure that every last missing scene or documentary is on the disc.