Building a 150$ great phone would allow them to set a feature/quality floor for the market. If they forced their suppliers so the hardware in these phones is properly supported upstream, targeting new versions of Android should be pretty easy. When Ubuntu launches a new version it doesn't need to go and retrofit it to the thousand different types of laptop out there. The state of Android though is that the GPU/Camera/whatever drivers are binary blobs locked in to a specific kernel version.
[1] https://developer.android.com/about/dashboards/index.html