They had some people on last night who said that these days it is not uncommon to not take credit afterwards. They said the heat goes up so much when a group takes credit it has started to scare them off from grandstanding anymore, so that part really isn't that odd.
Also they said the only way the transponder goes off is an electrical failure of epic proportions, or someone turning it off. And as far as the electrical failure, the plane is so advanced technology that would be virtually impossible.
Now that they are looking in the right place they will probably find this thing pretty soon. In about a million pieces.