Despite the traGedy, I am enjoying this thread and this mystery. The most entertaining posts are the ones writing novels about MH370, "below 500 ft they slowed to V1, landed and water seeped in through the cracks in the fuselage, then they sank".
The (apparent) lack of transponder data and comms means one of two things:
-MH 370 suffered a catastrophic failure taking out all electrics. Fast. What are the odds? Cockpit fire? No, not that fast. Not a decompression. Not a flight upset. A bomb, a missile or a midair.
-MH 370 was hijacked and systems switched off. By passengers or by the operating pilot(s). What happened after is anyones guess.
My money is on option #2.