Fares are based on market demand, neither distance nor connectability.
Shuttle fares are what they are because the travelers in those markets are, primarily, interested in the convenience of the schedule and the service and are willing to pay that fare for it. Unfortunately Art was caught between a rock and a hard place of loyalty to US and a much lower fare on B6. B6 charges a lower fare because they can't justify the higher one. US charges the higher fare because they can justify it, and people pay it.
And to CluebyFour's point about ontime between JFK and LGA, that's not the point I was making, albeit it's a good one. B6 has consistently ranked at the bottom of OTP industry wide, while US has ranked consistently near the top. The point is that a US Shuttle flight has a much greater probability of operating on schedule than either DL, B6, or AA based on overall reliability.
Jimntx makes the best point of all, though, and that applies to all markets, not just Shuttle. We can't get too comfortable in the fact that sometimes people fly a legacy instead of WN. It should be that our complete package of service is enough to put the thought of flying WN out of the customer's mind. We have a long way to go in that respect.