That's actually one of the more interesting parts about Angular. I'm not sure of the details but I believe the Angular team have been counting on Object.observe for increasing the performance of the Angular code [0] (something that Google / the Chrome team have influence over).
The Angular code you write now won't need to be updated and will get a great speed boost later. Other libraries, like Ember, get you to add all that metadata to your code to give you a performance boost now (which to me feels like something you'll regret in a year's time).
Actually, I'm sure it'll break a few things. Angular doesn't have a good concept of update granularity, which can be problematic when you get to the multi-directive interaction phase...
The Angular code you write now won't need to be updated and will get a great speed boost later. Other libraries, like Ember, get you to add all that metadata to your code to give you a performance boost now (which to me feels like something you'll regret in a year's time).
Ah, this is the post I was looking for [1].
[0] http://blog.angularjs.org/2012/07/angularjs-10-12-roadmap.ht...
[1] https://plus.google.com/112439678898563138768/posts/RZKRBiGX...