Some points;
Cryan charges £2/2€ per passenger ticket to cover the cost of their obligations under Regulation 261. They say they carried 79.6 million last year but that's passenger sectors (average ticket is out and back) so actual number of surcharges would be half that. Say €40 million. Even with the Volcano their expenses cannot be anything like this.
When the regulation was being written nobody (airlines/EC/EP) considered that a multi-day closure of airspace was even possible. Never happened before. (The Regulation is being considered for amendment by EC/EP and it could include, in hindsight, such provisions but don't hold your breath)
The Courts have agreed that the closure was an 'extraordinary circumstances' meaning that compensation for cancellation (€200~600) was not applicable. The courts have ruled correctly that, as written, the airlines do have an obligation for care (reasonable cost of meals and accommodation) and rebooking/ rerouting.
Yes the railroads have a similar obligation; See
http://eur-lex.europa.eu/LexUriServ/...14:0041:EN:PDF . Article 18 2 (b) clearly states an obligation to cover hotel costs for a stay of 'one or more' nights. I know the Swiss Federal Railroad regularly covers hotel costs when connections to last services are missed.
The airlines in theory could insure against these costs, but I don't know of any that actually do. Insurance companies expect to receive more in premiums than they pay out in costs. This means that even if it was offered it would be so expensive that no airline would be tempted. (The insurance companies would set their premiums based on a worst-case scenario - something like what happened in 2010)
Perhaps passengers could buy their own insurance, but I doubt if they could find a policy that covers all-risks. And why would they (to/from/within EU)? The EU requires the airline to cover these costs.
What I expect we will see now is other airlines adopting Cryan's '261 Surcharge'. Great money maker and would more than likely offset the costs they are required to cover, by law.