As the book states, models should not perform data retrieval as this should have been done before the model was returned by the business objects invoked by the web tier controllers.
How then do you propose tackling times when such large volumes of data need to be transmitted back that it makes sense to only transmit back part of the data?
For example, if an image to be sent back is large, it might be a good idea (performance wise) to only send back part of the image (the part displayed at first..say the upper left hand corner for instance). If the view then goes to the model requesting the lower right hand side, the model, not having this data, might then issue a request to retrieve this information.
So, in such an instance, does this seem appropriate, or should it be handled in another way?