Thumper, I agree that it seems strange that programs seem to be inconsistent about how they accept people. I guess what it shows is that most people who apply for MSW or post-grad BSW are probably EXTREMELY qualified; the same people are applying to both programs. Other than GPA, there must be a bit of luck involved in getting accepted - it is probably highly dependent on who are on the admissions committees and what they find appealing about people's applications. For example, I think U of T really likes research experience/academics but maybe the other programs prefer other kinds of experiences.
Unfortunately there are just so many people competing for not enough spots.