mrezee
Living the dream!
AA wholly owns regional airlines too; they own Envoy, PSA, and Piedmont. Since Delta also owns a regional, I can't see United sitting on the sidelines for long...
The difference is that AA has done the opposite and branched out from its one wholly-owned. Years ago, it used to just be American Eagle (now Envoy) doing all the flying. Then Chautaqua started as AmericanConnection. Then came Republic. And now after the AA/US merger there are quite a few carriers flying as American Eagle now. Envoy, in the process, lost a number of their 145s to ExpressJet and Piedmont, and their -700s are all supposed to go to PSA eventually (don't quote me on that as it may have changed since I worked there). DFW and ORD, which were almost all Eagle, have a huge presence of Mesa, ExpressJet, SkyWest, and PSA now.
On the other hand, the rumor floating around at my shop is that within 10 years or so, there will only be 3 Delta Connection carriers: Endeavor, SkyWest, and Republic.