Yes, not all geometries support multiple materials. The general philosophy of three.js is to keep things simple. Only some selected geometries use groups, where it actually makes sense. For example a Box has six clearly distinct surfaces that should be able to display different materials. But why would you want multiple materials on a sphere or torus? If users actually need these specific geometry data, they have to create them with 3D modeling tools like Blender. So multiple materials are not a must for procedurally generated geometries.