I wonder if there are good numbers on how many of those customers use public transit. NYC is rare among American cities where even wealthy people ride the subway. I'm not a wealthy J-class passenger using helicopter shuttles, but even if I'm able to afford a car service, the trains are usually about the same time (in traffic).

From Long Island, taking the LIRR to Penn station and hopping on the NJ transit to EWR would probably be about the same time as driving to JFK in traffic (although slower than taking public transit to JFK).

That said, United isn't in as bad a position as all this makes it out to be. As much as they miss out on eastern traffic that prefers JFK, there are plenty of rich people in NJ, and the same traffic concerns keep them from considering DL / AA / B6 at JFK. And Manhattan is competitive between EWR and JFK. Splitting a market as huge as the tri-state area isn't that bad of a deal.

I think where they're really at a disadvantage is on the CA-originating side. Most of those passengers aren't familiar with the geography of the area, and even if EWR is just as convenient, they prefer going to JFK because that's the "New York" airport that everyone knows. I think avgeeks on sites like this overestimate the level of knowledge the average traveler is willing to acquire about airports, especially out of their home region. They don't want to figure out how to get into the city from both EWR and JFK and then switch around on each trip based on fares. They know 1 airport, and that's the one they'll fly to regardless of fare. I'm guessing that's where United struggles. Heck, when I lived in the Bay Area, I'd marvel at people living in Santa Clara (5 minutes from SJC) who'd fight traffic on the 101 to fly out of SFO because they didn't care to even search for options out of SJC.