Research MBA Programs

I've been looking through various MBA employment reports, and rankings, and it appears as though Canadian MBA programs (even the top-tier schools) churn out graduates with salaries much lower than those of their US counterparts. I'm not even talking about Top 10 US programs - more like those in the 20 and below range.

For instance (source: Financial Times rankings 2012),
Avg post-MBA salary:

University of Western Ontario (Ivey) - $100k
University of Toronto (Rotman) - $94k
York University (Schulich) - $88k
University of British Columbia (Sauder) - $80k

compared to:

University of Virginia - $135k
Carnegie Mellon - $132k
University of Michigan - $130k
Emory - $125k
Georgetown - $123k
UT-Austin - $121k
USC - $121k

these are mostly regional schools too, and we're talking $40-50k difference in annual salaries... the US top 10 are in the $170-190k range but we won't get into that.

Obviously this is just a sample based on MBA employment reports but I had no idea there was such a discrepancy between Canada and the US. Does anyone know why this is? I always thought Toronto had fairly high average salaries but I guess that's not the case.