Link off of DF on how The Android Hardware-Buttons Are Broken.
The argument here is of course that Twitter is doing it wrong, that the back button should always bring you back one step inside the app, but that this inconsistency can even present itself in the OS shows a big conceptual faux pas when it comes to the Android UI.
Personally I have about 10 minutes total time with an android device, so I have no idea if this is apple fanboy flame bait or legitimate android conversation. It's interesting to see though, as I've never really thought about how the different buttons would work, as I'm not used to having them.