I don't find it particularly strange or amazing - very sad, yes, and my heart goes out to those waiting to hear about their loved ones.
OK, it's wrong to speculate, but a sudden 'disappearance' like this, without any distress call or other communication, to me points to one of two things - onboard explosive terrorist action, or shot down.
A news photo yesterday showed what looked like an emergency exit hatch floating on the surface of the sea, so a possibility of catastrophic break up perhaps?