Indeed this method will not be able to tell a cat from a dog, if they always occur in the same environment. However, I would not term this as 'breaking down' of the method as the motivation is not to do exact identification. Since their method is based only on global statistics of the image, it can be used as a **fast** pre-processing step for object detection. For example, in case of object detection, many images or large parts of images can be pruned out at the preliminary stage.

To acurately recognize an object (a cat or a dog), one can then do a local search on the remaining data. Performing local search can be very expensive, which justifies using this method for pre-processing.