Why do most photorealistic renderers have similar material test scenes? I notice that most photorealistic renderers have very similar material test scenes. Here are a few examples:

Blender



Mitsuba



Vray



My question is: why is this specific model / style chosen to test materials? Does it have some advantage over teapots, spheres, and suzannes? Are there other common scenes for material testing?
While teapot, spheres and trusty Suzanne are not per se bad test scenes for materials, here are some things to consider. You can apply them to said examples to forge your own opinion.

First and foremost, the viewer needs to be able to examine the behavior of the BRDF. Since it is dependent on both the direction of incident light and the direction from surface to viewer, you need to have as many combinations as possible in your test scene. A spheroid nicely covers all possible viewer angles.

Notice that all three scenes feature some sharper edges or creases too. Differences in reflective behavior across a smooth surface (like a sphere) may be hard to conceive, so these edges put emphasis on this.

Since the observed brightness and color is a combination of the material (i.e. the BRDF) and the lighting environment, it may be hard to tell one from another. The Vray test scene takes care of this. The 100% white 'core' and the 25% black floor help you get an idea of what the lighting in the scene is like.

Blender and Vray both feature a grid that helps you estimate the total size of the scene. This helps with evaluating grain or surface texture.



Here is a side-by-side comparison of a cube, notched sphere and Suzanne for a glossy test material with a slight normal map (rendered in Blender with Cycles, lit with the Dutch Skies 360 - Free 002 HDR):



The cube does a pretty good job on depicting the normal map. The sphere, as expected, is reasonably good for normals and gloss. Suzanne, arguably, makes both a bit harder to perceive than the spheroid.