Well, having watched the aviation industry for a while now, I have to admit to having some reservations about modern planes.
I believe I'm right in saying that the Boeing 777 is a 'fly by wire' aircraft, in which case, the pilots have no direct control over anything. More a case of 'ask the computer nicely and it will do what you want'.
Now, how often have you guys had either a complete system freeze or a 'blue screen of death' (BSOD) occur?
Supposing, just for arguments sake, that this (or something similar) happened to the the flight system controlling the engines?
It is certainly unusual for both to quit at once! Bird strike would kill one - two at the same time is stretching it a bit. Same for fuel, I'd expect one to quit way before the other (same for mechanical issues).
I suspect the answer will lie in the 'fly by wire' stuff - some errant signal told both engines to cease operation thus rendering the aircraft a glider and, since the modern jet has all the gliding characteristics of a house brick, the result was inevitable.
Let's wait and see - though there may be an attempt at a cover-up if too much money is involved on the part of Boeing (think class action law suits).