I pretty much agree with this.
As this thread has meandered my stance has changed a bit.
1) Airline tickets should be non-refundable. Like you say, if life happens, life happens.
2) If an airline wants to give a passenger a refund opportunity prior to, say, 5 days before the flight, that's fine, but it'd be purely voluntary of the airline. There would be no obligation or compulsion to do so.
3) If you buy a ticket, and you show up, the seat is yours. Period. Just like a ball game or a concert.
4) The airline can "overbook", but it'd be similar to the old "stand by" system. The overbooked passengers are the ones that may lose out.
There, solved.