Brian –
Lots of cities have public transit to the airport.
I lived in Philly and took the Septa to the airport.
I lived in Atlanta and took Marta to the airport.
I was in NYC over New Years – we took the airtrain from JFK to Jamacha Queens – then LIRR to Penn Station, then subway to our hotel. Waaaaay faster than a shuttle bus or cab – and cheap! (6 days in NYC and did it 100% public transit – not even cabs!)
My nephew who lives in the “valley” takes the metro to the bus to go to LAX. He doesn’t like to leave his car at the airport.
San Diego is backwards – but as you pointed out – you can take the bus from the airport here.
Good to know about Vegas – we always did the paid shuttle buses… but they were pretty cheap.