I think the first part of the original didn't suit the groove in the later version of the song.
There is live version from the '79 tour on a CD bootleg called 'A Song For Europe' that has a groove similar to the 'Horoscope' version (in a 1979 sort of way) and maybe Ferry felt that the 'groove' orientated era of his writing/recording was the right time to re-make and re-model Mother Of Pearl.
The later version was originaly intended for the film Basict Instinct. I am not sure if it was recorded specifically for this movie and that may have determined the approach to this re-recording.
http://www.vivaroxymusic.com/songs_326.phpJ.O'B.