Scott Fybush said:
TBS national and WTBS Atlanta were a nearly-straight simulcast right up until the relaunch of the Atlanta station as "Peachtree TV." Only the ads and some Saturday morning public-affairs programming differed between the Atlanta broadcast feed and the national feed.
I don't know Scott - last time I looked, WTBS showed a few of those programs in Atlanta that were subject to the syndex rule. This was just a few years ago, but WTBS did look to be quite different from TBS during the daytime while much the same at night. Hate to argue with you (because I hate to lose) so I'll grant you 2 things for certain on the subject:
1) TBS has managed a number of syndication deals for shows (such as Seinfeld and Friends) which allowed it rights both nationally and in Atlanta as a local station;
2) Because of this, there was a lot more duplication on WTBS/TBS just before the flip to WPCH than what you see on WGN/WGN America.
But WTBS did have some other shows that were only shown locally. After 1996, there was a bit of a separation between feeds.
Scott Fybush said:
It's not quite that simple, and the "fools" at Wikipedia aren't quite that foolish. At least where the FCC and the Copyright Royalty Tribunal are concerned, there are some specific meanings to "superstation," allowing the handful of stations with grandfathered superstation status to be distributed in ways that other local stations are not. The specific rules are enshrined in 47CFR76.120, and WGN is included as one of those "superstations." I'm not a communications lawyer, so I won't pretend to be able to explain how WGN America can still provide a nearly completely different program service and still qualify, but it does.
Perhaps 'fool' was a little too strong of a word that belies the mood I was in after reading gregg75's post.

But Wikipedia isn't always correct either.
Most of WGN's schedule (locally, in Chicago) consists of programs that would be syndexed out on cable systems all over the US. Those programs, plus their CW fare and some sporting events, are all shown only in WGN's home market. That represents a radical change from the WGN satellite feed of, say 1995, when almost everything was shared between the local and sat feeds. At this point, WGN and WGN America have very little programming in common - basically the 9 PM news and a couple of shows that don't violate syndex. And a few specials such as WGN's airing of holiday parades (Tournament of Roses comes to mind - though it's actually KTLA's coverage that's used).
Personal opinion about why it's still WGN America: because so many cable systems have had WGN for so long that they wanted to use the name to make sure that the channel isn't dropped. With some Cubbies games and WGN News at 9, they can still reasonably get away with it in most of the US. In other words, a great marketing tool to cable systems and viewers that plays on a legacy brand and Chicago connection. Truly, it's a great idea in today's marketplace - but I don't know that I'd consider it to be a superstation either. Not really.