The reason that so many rendering API's are supported relates to coverage. In the context of an Android app store it is the percentage of apps that can be supported via remote rendering. You would like to remotely support a large percentage of unaltered apps as they currently exist in the app store.
The above Venn diagram illustrates the overlapping coverages for each rendering API. For example: to support Java ICS apps, which render to OpenGL ES 2.0., it is sufficient to support the yellow OpenGLRender API (¬). To support a Java Froyo app the green Canvas (¯) or blue Skia (®) API is sufficient. More sophisticated apps might need red OpenGL ES 2.0 API () support.