Both sides have a point.
But that is what insurances should be for.
In the Icelandic volcano case the insurance companies hided also behind the " act of God" and for the vast majority did not compensate their custommers stranded pax.
Having been on the wrong side of the Atlantic at the time the thing erupted, I could watch first hand how the various airlines coped with it.
The very good ones ( LH, DE among others) sent regularly SMS to their pax, keeping them informed and then sent empty aircraft to take back the starnded pax once the airspace was open. ( I was with them fortunately)
The good ones,( the majority) diveterd flights to take slowly the load and re-routed their pax on other airlines.
The bad ones just resumed the normal flights and only took stranded pax back depending on the free seats on board. That took days..
The very bad ones did not bother and offered refund of the cancelled flights , up to you to find a seat back. Some were stranded 10 days .. Some Government charetered aircraft to get their people back.
If you had money , no problem , but if you were a family with 2 kids and your holiday budget was gone, and of course you were on the cheaper last category airlines, this was tragic. I saw complete families sleeping in the terminals, begging for food and water.
How you treat your pax should make you chose your airline, but we know that, not the average pax. So I understand the ruling.