I'm assuming here that the story is correct for debating sake. Whether it is or not is to be determined.
"I believe Boeing, and many other aircraft manufacturers define their requirement for deicing as "OAT less than 10 degrees Celsius and visible moisture" with "no ice or snow adhering to the wing surface."
Not sure about Boeing but is not exactly correct for Airbus. As per Airbus FCOM,
"Icing conditions may be expected when the OAT (on ground and for take-off), or the TAT (in-flight) is 10 degrees C or below, and there is visible moisture in the air (such as clouds, fog with low visibility of one mile or less, rain, snow, sleet, ice crystals) or standing water. slush, ice or snow is present on the taxiways."
For operation of the engine anti-ice system, pilots must turn it on with the above criteria are met and not wait until they see ice building up. It's slightly different for de-icing and/or anti-icing of the critical surfaces. In this case, all critical surfaces must be clear of snow, frost and ice for takeoff.
Why wasn't the aircraft sprayed/deiced? Captain's responsibility. Captain's call.
Yes and no. Usually the FCOM will stipulate that in all circumstances, it is the Captain's responsibility to decide whether or not to de-ice/anti-ice the aircraft, or to order a repeated treatment.
But many companies go a little further and include in their operations manuals (excerpts from our Operations Manual and Route Manual):
No aircraft will be released for take-off from any station until the flight crew and the qualified de-icing person, as dictated in the contractor’s Standards and Procedures Manual, are satisfied that the critical surfaces are free from frost, ice and snow.
Flights may be dispatched when it is agreed by the Captain and the Qualified Person that the snow on the surfaces is light, not adhering to the wing surface and is of such consistency that it will blow off during taxi or the immediate start of the take-off roll. However, such snow should be blown off using dry unheated air or nitrogen wherever possible prior to dispatch from the gate.
The reverse of cold soaking can take place when dry, cold snow encounters wing surfaces warmed by fuel pumped from underground storage, the snow may melt and re-freeze. As is the case for cold soaking, the hazard may not occur until just prior to take-off. Remember, underlying snow or slush can be a layer of clear ice.
The decision to de-ice may be made by a Qualified Person or by the flight crew. However, once the decision to de-ice has been made, it cannot be over-ridden by the other party.
The clean wing concept is an excellent rule. When flying these bigger aircraft, it's extremely difficult to assess if snow is adhering or not to the surface. Why chance it? Get sprayed, you have many, many lives depending on you, not to mention your own skinny rear-end. The evidence is overwhelming about what can happen if you takeoff with a contaminated wing. The manufacturer, the company, and the governing authorities give vasts amount of info about operating in icing conditions. If after taking into consideration all this info, I'm still not 100% certain if I should spray or not, then I spray. Safety is paramount and I'd rather err on the safe side.
To attack the crew in this instance for NOT deicing is folly. I'm sure the Captain considered the "usual" pre-departure stuff and decided not to deice. That's the end of it. Discussion over.
Why should he have to defend that decision. Obviously it was the right one because the flight not only operated safely from A to B but is history.
I could not disagree with you more. I don't condone attacking the crew, but an investigation is warranted if the story is correct. Again if the story is correct then I sincerely believe that it was the wrong decision, as stated by the fact that contamination still existed after takeoff. Just cause a flight arrives at destination does not mean it was not in any potential danger at some point. Being a captain means being the one responsible and having to answer for your decisions. Should you ever have to answer for your actions then hopefully your answers will be the right ones. If not, then he/she/we must learn from the mistakes in order to avoid them in the future. In some cases that requires extra training. It's not about hanging anyone out to dry, unless true negligence or diseregard for the rules/procedures was exercised; it is about safety.