That's because Garmin bought out Navigon.
I'm not sure if Garmin changed their app but the main difference between the two when I was researching GPS apps was that Navigon stored its maps on your phone where as Garmin required a cell signal. In my travels I sometimes ventured out of cell range and using it for GPS was going to be problematic.
I think for apps Navigon is the better app based on reviews and others recommending but it is a personal preference.