Can a journal withhold referee reports from the authors of a rejected paper? We submitted a paper to a journal published by Cambridge Press. The paper was submitted last year (2013). After five months we got the decision yesterday. We don't mind the decision, however, we are shocked by the editorial comments that although they have the reports they don't relay the reports to the author/s for papers which are not proceeding further. Is this approach common in journals? We feel this is very unethical from any author's point of view.
I consider that not giving authors the ground on which the decision was taken to be both unethical and bad for science. How should the authors improve the paper if they don't even know why they have been rejected? How can they get a sense of what the community expects from them?

I am not alone in this: the International Mathematical Union issued ethical guidelines for journals, including that the default policy should be that referee's reports are forwarded to author. However many journals give the referees the opportunity to give comments solely for the editors, and some editors prefer not to forward some reports to avoid pissing off the authors. I never heard of a journal with a policy of never forwarding reports of rejected papers before; this sounds absurd or really cowardly.