As someone who works with .NET at work, I can tell you that the API churn there is incredible. And I think everyone is aware of how often OSX has changed APIs and how difficult it has been to switch from Carbon to Cocoa. So i find complaints about Linux APIs changing too much to be a little humorous.
Oh yeah what a freaking change has that been <_<'
Get outa here, troll... Cocoa is a rename of the Unix cross platform API that came from NextStep. This universal API is now (freaking finaly) implemented on Linux in the form of GnuStep.