Was the paid market for RSS readers really that big before Google Reader? There were tons of free readers (as you say, it's a pretty simple product to make). I don't remember any big-name paid RSS readers.
NetNewsWire was huge if you were a Mac user, and was released in 2002. NewsGator had a Windows app and paid syncing service, and bought NNW (it's changed hands a few times, now at Black Pixel). Both of these predated Google Reader and were paid apps.
There are also plenty of paid apps in the mobile space that sync with Google Reader.
