i should have also added:

with FLARM, the aircraft move slowly, and they are all VFR, so having relative position and altitude from a non-certified, low-res source is still fundamentally useful for improving see-and-avoid (although not necessarily for IFR separation)

On Tuesday, February 24, 2015 at 10:36:13 AM UTC-5, Bob Pasker wrote:
I wonder if the reason for requiring high-resolution TSO'd GPSs is that ADS-B will be used for IFR separation and for fast-moving aircraft, so high-resolution position and updates is an absolute requirement, a la fast-scan radar.