1. Documentation for ImageWriter.getDefaultWriteparam() says that the default implmentation of this method returns an ImageReadParam.

2. It says that a new ImageWriteParam will be returned which does not allow
tiling, compression or progressive encoding but actually the returned WriteParam supports progressive Encoding for JPEG and PNG as it is supported by the respective plugins. When this method gets called what is actually returned is an instance of the subclass of imageWriteParam available in the plugin and the value for the above features are purely dependent on the plugin implmentation. Any user who uses this method would just expect false for the above features(tiling, progressive encoding etc) but the return value for the above features will be totally plugin-specific.
Hence it could be mentioned that the support for tiling, Progressive Encoding etc depends on the plugin that will construct this object and not just ImageWriteParam class.