At the risk of harping on and on, I would like to close the debate with this ...
Yes, we do know that Google Street is a volatile place, but for me and from what I gather a lot of others with long term, stable (even authority sites) which are strictly by the book, white-hat, following every guideline Google gave us, have weathered the worst that Google has thrown at us (florida, big daddy etc) with no ill effects, this new change (which from my perspective is by far the most major I have ever seen) was completely unannounced and unforeseeable.
My business can and will survive on reduced serps, but when you have had a 'free handout' of traffic/sales, to have it suddenly stop without warning is very disturbing, no matter how well founded and stable your business.
Google managed to make a big thing out of Caffeine (despite the fact that they claim that for most websites there would be little or no difference to most webmasters), but when it comes to something of the magnitude of Mayday there is nothing except for a miserable youtube video from MC weeks after the event.
Google have no legal obligation, but they do definitely have a moral obligation.