Unctuous:- I am sure that Al Qaeda don't need your help in trying to find various weak points in air security. You also said
>>After a while it becomes SOP for all air-crashes to be assumed prima facie to be Al Qaeda accomplishments - nice force multiplier effect. <<
That process depends on people like you giving credence to these wild speculations. It is not a simple matter to put explosive devices into airfreight, and the unpredictability inherent in much freight handling would make it a very unreliable weapon to target. Ask any freight dog...
Your other speculation about ignition of fuel vapour may be a more likely scenario, but that should be revealed by an investigation.
I have 2 worries about the accident and its aftermath:-
1) Taiwan has just completed its first accident investigation, and anyone who knows the status at Taipei airport prior to the SQ accident will realise that the report was a whitewash of their own culpability at the expense of the SQ crew. This does not bode well for objectivity.
2) Taiwan is so dependent on US support that they could get browbeaten into a compliant report that exonerates Boeing if the fuel tank scenario is confirmed.
The big plus this time is the apparently shallow water at the crash site(s), and the likelihood of finding lots of evidence.