Just like it happens with cars, obscure plane parts wear out. Take for example an incident that happened in 2008, when a 747 cable burned out after the protective covering was worn off due to friction against a bolt.
Take a look at this final report on this 747 smoke event on Eva Airways Flight BR67 at Bangkok Suvarnabhumi International Airport.
Prior to this event, Boeing had sent out a service Letter to inform operators of the potential fire hazard from the arcing of a wire bundle which might result in a fire on Corrosion Inhibiting Compound (CIC) contaminated insulation blankets. They predicted it. It happened.
So as we think about Malaysia Airlines Flight 370. There is always the possibility that some small component like the one below failed, and led to something catastrophic. What if the pilots were overcome by smoke in the cabin? I am not saying that this DID happen, I am only saying there are myriad small parts that can lead to catastrophic events. It makes sense to look at any and all Boeing 777 safety advisories, in case they might predict some small event that cascaded into disaster.
Thanks to input from John King.