Most types of digital Anti-Aliasing (Multi-Sampling or Super-Sampling) only appily the effect where it's needed, and can even bring out detail in a digitally rendered image that would not have been there otherwise. It maintains sharpness while fixing certain problems.
The AA filter on a camera would be comparable to a post processing AA filter, like FXAA, which simply blends every pixel on the screen with its neighbour, which eliminates both aliasing and crisp edges.
Sort of but multi-sampling covers the entire scene so it does it's thing everywhere, but the effects are obviously more noticeable on some parts of some images than on others (unless they did some targeting to located areas of harshest transition and only multi-sample those regions).
The reason multi-sampling is so much more efficient than super-sampling is that it's applied selectively.
That also means it's less effective in some applications, but the cost to benefit ratio is very attractive.