Charper i don't think thats the deal as wgn9 and wgn super is totally different, even though they air allot of the same programming. I think the deal tbs and peach tree is that it was two of the same like how wgn is now, but separated into two completely different stations that ended up picking up equal rights to the games, but sense peach tree was a local channel, something had to contractually worked out.
With WGN, the games air locally also air on superstation. Sense the station is owned by both and not separate this doesn't apply as D* can just show the national feed and not mess with any local feeds.