Pretty much this. AngularJS abstracts DOM manipulation away from the user; by adding React to an AngularJS project, you're giving up on that abstraction. I consider React a sacrifice of abstraction / ease of development in favor of performance.
I think AngularJS will adopt a similar strategy for their 2.0 development effort, maybe even a 1.x point release. But I haven't looked at the angular development process for a while now.
I disagree with this. React abstracts away DOM manipulation just as well as Angular does at a high level. When you dive deeper (i.e. building components/directives) React continues to abstract it away, whereas Angular reveals it.
In fact, React is able to get superior performance because the DOM is abstracted so far away.
I think AngularJS will adopt a similar strategy for their 2.0 development effort, maybe even a 1.x point release. But I haven't looked at the angular development process for a while now.