if they are making this public... imagine what they're testing that they aren't making public? 
Nah, thats all they got
They need to scare the chinese as much as they can
In my opinion, this is just mind games with the chinese. Convenient how both of the prototypes lost contact and self terminated. I think it's to scare everyone about the tools they have available, a bit like the cold war.
As Guy said, this *should* be strictly confidential stuff only known to US government but they're broadcasting it? I'm sure behind the scenes somewhere secret there's stuff being developed and tested that we can only imagine seeing in terminator, harry potter (Invisible cape) and star wars. There was a rumour a while back that the US government had developed and tested an invisibility device. The trick is to make the light bend around it, thus making it invisible. The device was only capable of making an object the size of a grain of sand invisible, but the fact that they got as far as making a grain of sand invisible is enough proof that with time there will be tanks roaming around in foreign countries completely invisible to enemies.