Actually I'm not surprised that you didn't have a problem. First of all, you didn't really want a refund, you simply wanted to book the correct trip and one that was comparable in cost.

Next when traveling on the corridor, normal rules for exchanging tickets including the fees normally charged, don't always apply. The only thing one has to watch out for are first class reservations on Acela & the Metroliner.

Finally even with the most restrictive fares, if the ticket(s) have not yet been printed, things are easier to fix. Once the ticket(s) are printed however, it gets a lot harder to fix things without penalties if it's even fixable.