Developing a web application using a SPA framework requires skills in both JavaScript programming and HTML + CSS design. Sometimes, these are the same person, but quite often, they are not, and people with different skill sets do collaborate via the same framework.
In fact that is one of the major advantages of using any SPA framework: They enforce a structures and patterns for organising code and other assets within the code base for the application, leading to more consistency and easier collaboration when developing in a team.
Templates are where most of the overlap happens to be, and thus where the collaboration, between programmers and designers needs to occur.
Thus with EmberJs, the decision about where the separation occurs has already been made. However, with AngularJs, the decision on where to to draw the line is left up to the programmers and designers to work out themselves.