Since these films were animated at 1.66:1 they are probably just as cropped at 4x3 as they are to arrive at 1.77:1 on BD. They just cropping from a different direction.

While I can't speak from haven't actually compared them, I would think that the Lion King's AC3 track is probably a blunt copy of the original theatrical mix.

Laserdiscs were a limited market enthusiast medium. Studios rarely saw a need to spend the time remixing a track when the home theater systems they would play on could handle them fine.

The stereo track is probably just a downmix meant to handle TV speakers better.