In the Khronos documentation support for the glGenerateMipmap(GLenum target) function starts with OpenGL 3.0. Why then does this function also exist in the GLES20 class?:
GLES20.glGenerateMipmap(GLES20.GL_TEXTURE_2D);
Or does OpenGL ES 2.0 also support the automatic generation of mipmaps?
The page where you refer to, is not a specification, it is a wiki. Further more you refer to the desktop OpenGL pages rather than the OpenGL ES pages.
The glGenerateMipmap OpenGL ES page, clearly states that glGenerateMipmap is provides since OpenGL ES 2.0.
Anyway, the only truth is the OpenGL (ES) specification.
See OpenGL ES 2.0 Full Specification- 3.7.11 Mipmap Generation:
Mipmaps can be generated with the command
void GenerateMipmap( enum target );