If you buy X to Y, then US is contracted to get you from X to Y. Any intermediary stops are arbitrary.

If there's weather, provided there are flights, US can simply fly you X-DCA-Y or X-PHL-Y. There's absolutely no reason to go to/through CLT.


On one occasion, I was flying PHX-PHL-AVP, and the PHL-AVP leg was extremely delayed due to weather in both PHL and AVP. I asked about skipping that leg without my return trip cancelled, and the US agent said that I could if I wanted to.
After checking on changing my car rental, I decided to stick it out, as the drop fee would have been absurd.