If I had to make a guess, I would say that this change was made for reasons totally unrelated to performance.
First, modern GPUs are capable of handling millions of triangles with ease. Games are almost never vertex bound. They are usually pixel bound or bound by locking. In other words, too many or too costly of pixel operations are in use or there is some poor coordination between the CPU and GPU where the CPU gets stuck waiting for the GPU or the GPU is underutilized at certain times and then over burdened other times.
Adding two maps adds two texture fetches and possibly some blending calculations. It's very hard to weigh the comparable impact because different situations have a huge impact on which code gets executed.
For a model with many triangles, the word case scenario is seeing the side of the model with the most faces. This will cause the most triangles to pass the winding test, occlusion tests, frustum tests, etc. This will be relatively the same regardless of how close the coin is to the camera.
For the normal mapped test, the worst case scenario is when the coin fills the view regardless of its orientation. This is because the triangles will then be rasterizied across the entire screen resulting in a coin material calculation and therefore the additional fetches for every pixel of the screen.
Also, when it comes to quality, normal maps have a tendency to break down at views of high angular incidence. This is because though the lighting behaves as expected, it becomes clear that parts of the model aren't sticking up and occluding the coin. This means such maps are a poor solution for things like walls on long hallways where the view is expected to be almost perpendicular to the wall surfaces most of the time.
There is a solution called Parallax Occlusion Mapping. Though it is expensive and I don't see it in a lot of games.
First, modern GPUs are capable of handling millions of triangles with ease. Games are almost never vertex bound. They are usually pixel bound or bound by locking. In other words, too many or too costly of pixel operations are in use or there is some poor coordination between the CPU and GPU where the CPU gets stuck waiting for the GPU or the GPU is underutilized at certain times and then over burdened other times.
Adding two maps adds two texture fetches and possibly some blending calculations. It's very hard to weigh the comparable impact because different situations have a huge impact on which code gets executed.
For a model with many triangles, the word case scenario is seeing the side of the model with the most faces. This will cause the most triangles to pass the winding test, occlusion tests, frustum tests, etc. This will be relatively the same regardless of how close the coin is to the camera.
For the normal mapped test, the worst case scenario is when the coin fills the view regardless of its orientation. This is because the triangles will then be rasterizied across the entire screen resulting in a coin material calculation and therefore the additional fetches for every pixel of the screen.
Also, when it comes to quality, normal maps have a tendency to break down at views of high angular incidence. This is because though the lighting behaves as expected, it becomes clear that parts of the model aren't sticking up and occluding the coin. This means such maps are a poor solution for things like walls on long hallways where the view is expected to be almost perpendicular to the wall surfaces most of the time.
There is a solution called Parallax Occlusion Mapping. Though it is expensive and I don't see it in a lot of games.