Short answer - it isn't.
172guy. You couldn't be more wrong. There are a number of Angel Flight operations in the US that operate quite similarly to Australia.
Angel Flight West | Angel Flight West is a nonprofit, volunteer-driven organization that arranges free, non-emergency air travel for children and adults with serious medical conditions and other compelling needs.
- AngelFlight.com ? People Helping People in Need
The US based AOPA provides support for charitable flights:
Guide to Charitable/Nonprofit/Community Event Sightseeing Flights - AOPA
Its all quite well organised, and anyone who is familiar with the Australian operation knows that it revised its pilot qualification & recency protocols some years ago based on its leaning from the US organisations.