As I understand it, US-applicants to Ottawa often receive no e-mail contact at all if everything goes well. Since Americans are visa-exempt, the originally-supplied passport copy is enough to issue the COPR. Someone who does not check eCAS may hear nothing from sponsor approval until the COPR arrives at a much later date.
I would not yet worry. Looking at the spreadsheet, user saria1 only yesterday received their COPR, yet their eCAS showed DM on the 11th.
Not a chance. Absent an infringement of liberty or racial discrimination, immigration applicants are only given a right to procedural fairness. That mostly means that CIC has to have a procedure, and they have to follow it. In practice, it means that their decisions must have reasons, and that they cannot be arbitrary or act with malice or in bad faith.
Other than that, there is no legal or constitutional guarantee to any specific performance standard, and moreover even if there were such a guarantee it would not apply here: our applications (you and I apparently applied within the space of a week, with my application the elder) haven't even come close to the 16-month 80% processing standard that was published at the time of our application. While we have every right to be annoyed that CIC is failing to meet their own 6-month processing goal, this is cause for an angry letter to our MPs rather than a lawsuit.