The ones I do see are typically freight carriers (FedEx, etc), or international airlines (Virgin). AFAIK, most of the flights into and out of this airport aren't those types. So, of the air traffic I do see, the majority don't identify with more than identifier and altitude. Lat lon is few and far between.

Regardless, his statement is true that ADS-B is not sufficient for full coverage in the US right now. I've seen estimates as low as 25% for the proportion of US carrier aircraft currently ADS-B. FlightAware in particular uses far more than just ADS-B.

Can you share how many and how far away? Are you near an ADS-B ground station (which will rebroadcast all traffic if a single ADS-B squitter/output is near) or only receiving active output from airplanes?