And -- wonder of wonders -- the cause of delays has dramatically changed in the past year (by an order of magnitude) for EU airlines. The causes under the control of the airline (and subject to compensation) have dropped to almost zero, while the causes not under the airline control (requiring no compensation) have risen (almost by the same amount, what a coincidence). The regulators have decided to look the other way, following BA's 3-engine 747 flight LAX-MAN (didn't quite have enough fuel to reach LHR) and the argument that rigorous enforcement of the EU compensation rules will lead to airlines operating flights in an unsafe condition just to avoid paying the compensation (for the LAX flight it would have been close to a million euros). All the "gray" area delays are now non-compensable.

The downgrade compensation is up to 75% of the purchased sector price. Of course this is the rub (the allocation of OWE ticket price to sectors is a trade secret). The law is summarized at
http://europa.eu/scadplus/leg/en/lvb/l24173.htm

EU rights poster (airlines are supposed to display this at all gates, but I've rarely seen it): http://ec.europa.eu/transport/air_po..._poster_en.pdf

Enforcement and more info: http://ec.europa.eu/transport/passengers/air/air_en.htm

As mentioned it specifically does not apply to agents, only to airlines regulated by the EU, so it would never apply to non-EU airline departing a non-EU city (even if arriving to an EU city), no matter how ticketed.

Downgrade is compensated at up to 75% of the sector price (of course this is a problem for OWE tickets as the sector price is a trade secret).
http://europa.eu/scadplus/leg/en/lvb/l24173.htm