From my travel agent days I can tell you that there exists, in fact, a “use it or lose it” bargain fare on most major airlines. They farm the tickets out to travel sites like Expedia, Hotwire, et cetera- and you get zip for cancelling- but these are relatively rare clearance fares and usually accompanied with BIG RED letters stating all bookings are final.
Outside of that exception, very few standard fares are refundable as in getting your money back. As Diosa said, most airlines allow you to retain credit for the value of your ticket less the change fees.
I agree with the majority. If you assumed the cost of the trip to attend a non-mandatory social event, then it’s your dime. I would be cheesed, though. I don’t have a travel budget and it is nearly impossible to get time off work. It’s even harder to give it back if you do happen to get it. In those shoes, I guess I’d stick with the trip and treat it like a little vacation without the pesky wedding to attend. Maybe find a concert or museum in the area, play tourist, and invite the dejected bride (or groom) out to commiserate. No way would I ask for money.