Why did Joss want them released in fullscreen? The season 4 episode in which Oz comes back reveals the answer -- near the end, when Oz and Willow embrace in the van, there is an obvious shot continuity "mistake", where one of the characters -- out of frame in the fullscreen version but not in the widescreen one -- leans in to hug the other, and then the camera angle changes to a wider shot and they haven't moved yet. The series was edited with a fullscreen ratio in mind, which is why mistakes like this could occur with things that aren't supposed to be seen on screen.
Why did Joss want them released in fullscreen? The season 4 episode in which Oz comes back reveals the answer -- near the end, when Oz and Willow embrace in the van, there is an obvious shot continuity "mistake", where one of the characters -- out of frame in the fullscreen version but not in the widescreen one -- leans in to hug the other, and then the camera angle changes to a wider shot and they haven't moved yet. The series was edited with a fullscreen ratio in mind, which is why mistakes like this could occur with things that aren't supposed to be seen on screen.