Wetfeet, you are quoting from the preamble to the Regulation rather than any part of the legislation itself. If you go down to the Regulation you'll see that article 5 paragraphs (1)a) and (3) together with articles 7, 8 and 9 make it explicitly clear that only the right to compensation is waived in the event of 'exceptional circumstances' like the ones you describe.
The right to care, as well as the right to refund or re-routing, persists even under these conditions.
Wetfeet, you also need to look at the next paragraph of the preamble:
(15) Extraordinary circumstances should be deemed to exist where the impact of an air traffic management decision in relation to a particular aircraft on a particular day gives rise to a long delay, an overnight delay, or the cancellation of one or more flights by that aircraft, even though all reasonable measures had been taken by the air carrier concerned to avoid the delays or cancellations.
This pretty well excludes an airspace closure, which doesn't apply to a particular aircraft on a particular day.
Even Cryanair agrees, the Regulation requires them, in these circumstances, to provide a refund, rerouting and care; but not cash compensation.