You didn't really rebut anything in his post, just asserted that Angular is 'forward-looking.' EvilTrout makes very specific claims, as someone quite familiar with Angular, you're well-poised to give a real answer, not just chest-puffing.
In my opinion this sucks. I love being able to use plain old javascript objects in Angular. Not having to extend every object with ember.observable is a big win for me. When O.o lands Angular will be just as fast (if not faster) as Ember but without the need to instantiate new Ember objects, and always use get() and set() on them.
Of course Ember could change its API in the future, but Angular won't need an API change because its already using plain old javascript objects.
While I'm with you and love being able to write my own simple classes and POJOs, ultimately I'll value being able to support users who won't or can't upgrade their browsers.
I also question your assumption that Object.observe will be as fast as Ember's observation system. I wouldn't be surprised if it was several times slower.
Object.observe also doesn't support array observation, which is something we support in Ember.