Update
I was happy to either get a refund or a UA travel voucher which I did get. The $100 travel voucher plus the meal and cab voucher = the amount of the original ticket. Interesting that you say that airport CS was told to have the pax contact customer relations for a voucher or refund. Where as when I called customer relations, they told me the airport was supposed to "compensate you" themselves. I would imagine the airport has the ability to issue the travel vouchers which would make the process easier and less time consuming, and I imagine since the vouchers are electronic that they append to the PNR from which they are issued to generate a paper/compensation trail on the record.
Incidentlaly I first heard the "trip in vain" term from US Airways. I called them to clarrify there procedures. E.g. I said what if a pax flew from BOS to LGA and got to LGA so late that they were going to miss whatever they were going to do in LGA. The rep said that as long as it was clear that the pax got on the next plane out of LGA back to BOS (in other words they did not go in to the city for a short while) they would issue a trip in vain refund even though both flight coupons were "used," since you just went to LGA in vain and had to go right back to BOS without leaving the gate or airport.
I'm sure trip in vain (or whatever each airline calls it) is normally only done if the pax brings it up. I'm sure it is not often volunteered.
But again for people that take east coast short one day trips it could be something you want to get familiar with because right now there are major delays almost evry day this summer on the east coast.