for visa exempt applicants, it's normal for some not to receive PPR. From what I've observed, this is usually because the copy of the passport submitted with the application shows 1) a validity date more than 6 months from the time of approval 2) it is unlikely the PR applicant will change their name (it seems men and women who have changed their names already are the ones waived PPR). Also, additional passport pictures are not necessarily requested because those are submitted upfront with the application. Applicants who had their application forwarded to another visa office for overflow issues (ie: london to ottawa) may get an additional picture request because it's assumed the file is sent electronically and the original pictures are not sent to the new visa office. as canuck suggested, some visa exempt applicants simply get their COPR in the mail.
