It's not like it was a mere 4 years ago, when Verizon locked down access to the GPS functionality on my Blackberry, preventing me from using it with anything other than VZ Navigator, including the Blackberry Maps app. If they want to charge a monthly fee for using the app, they're entitled to do so. There are back end costs involved with providing the service (servers, map updates, traffic data, etc), so I think it would be unreasonable to expect them to provide the service for free, even though others are doing just that.
For me, I did pay for a navigation app - CoPilot Live Premium. Is it great? No. But it has features that few others do, including the ability to add custom POIs, specify type that keeps me off roads I'm not supposed to be on with a commercial vehicle, and it allows me to avoid roads along the planned route if I choose. In my personal vehicle I Google Maps almost exclusively, if for no other reason than CoPilot's integration with the OS (i.e. clicking on address links in an email or calendar entry, or being able to use voice command to "navigate to...") is non-existent.