The GPS 20A meets the standard. But it is not TSO'd for use in certified aircraft. As such it is for use in experimental aircraft only here in the USA, just like the uAvionix Echo.
So it sounds like the Aussies get it. Think about it, imagine two aircraft shooting conventional ILS instrument approaches to minimums to parallel runways at the same time. One is an experimental aircraft with a GPS 20A providing WAAS to an Echo, a Stratus Transponder or Garmin GTX x35(r), and the other aircraft is a type certified aircraft with a TSO'd WAAS source providing position information to a GDL 82, Stratus Transponder or GTX x35(r). How could there be a real problem between the two sources if they are allowed to fly next to each other in IMC? Just because one says Experimental on the panel doesn't mean it's not as safe to be right next to another aircraft that doesn't say Experimental on the panel. So why the big hang up between "meets the standard" and "is TSO'd"? Even LSA's properly equipped can fly in IMC under an instrument flight plan in the same airspace as airliners.
It's the FAA--it doesn't have to make sense. But part of it is a quirk of ADS-B installation rules, and the general rules for installing equipment on certified aircraft. Look up AFS-360-2017-1
Short story is, the FAA generally only requires "meets the standard" for ADS-B equipment and position sources, regardless of aircraft. But getting the approval to
install the equipment is a different matter.
In general, installing something on a certified airplane usually means either getting an STC, or installing TSO'ed equipment (see Part 21). The FAA has issued guidance specific to ADS-B equipment to expedite installation. Provided the "initial equipment pairing approval" for position source and ADS-B Out device has been approved via TC or STC (on any aircraft), subsequent aircraft can install that equipment pair via 337 without specific approval, provided a few other conditions are met. It still does not directly absolve the need for a TSO'ed GPS unit of some kind, by a strict read of the policy (see item 3.b of the document listed above, although that sort of contradicts the flowchart later on where it says "meets the performance requirements of..."). I think this may have been an oversight?
However, note that an STC allows you to basically bypass the requirement for a TSO. If you can get an STC applicable to your aircraft that covers the pairing of your non-TSOed position source and non-TSOed ADS-B unit, you're good to go. That's how Dynon is able to use the Skyview GPS for ADS-B out--they obtained an STC including that equipment.
Technically, I don't think IFR navigation strictly requires an actual TSO, either; I think there's a provision for "meets the performance requirements" there, too. But those requirements go beyond just position and into things like database integrity, correctly computing routes, etc. So far, nobody* has come out with an IFR navigator that meets those requirements but isn't TSOed. I think that's a market thing--the market for non-TSOed ADS-B is big, because it can cover almost any aircraft, certified or experimental, IFR or VFR. But for all practical purposes, a non-TSOed IFR GPS would be limited to IFR homebuilts--a much smaller market with a smaller proportion of IFR-equipped aircraft. By getting the TSO, you get much easier installation on a much larger market.
*GRT is working on it, apparently, but no indication of when it will be ready...