I agree that it seems strange and unlikely that any audio engineer mixing music for CD/vinyl/tape in 1997 would even be thinking about potential DPLII upmixing benefits, but on the other hand - wow, this upmix sounds pretty amazing for what is likely to be a result of happy coincidence!
I hope I'm not breaking any forum rules by posting this here, but here's a FLAC of just the right surround channel from "Paranoid Android", for those who'd like to take a listen:
http://1drv.ms/18GABEq
(I assume posting copyrighted material is generally a no-no, but I'm hoping that posting just a single rear channel derived from DPLII is derivative enough to be considered fair use for illustrating a point. Moderators, please correct me if I'm wrong.)
What impresses me about this DPLII upmix is how well individual instruments and voices are isolated in the rear channels, almost discrete-like. There's little to no bleeding of the lead vocal and drums into the rear channels during the entire song.
Specific examples of well isolated elements:
00:00 - 02:12: percussion (maracas?) and electric guitar(s) only
02:22 - 02:31: twice you can hear a very audible vocal "huh-huh" over the bass line - I don't think I ever even noticed that before until I listened to this channel alone!
03:33 - 05:38: backing vocals completely dominate the rear channels during the mellow "Rain down..." segment
This is a little better than the average DPLII upmix, is it not?