You can correct me if I'm wrong, but I presume when the Canadian dollar was 65ยข and the U.S. had these exemptions for its own travellers, the Retail Council certainly wasn't concerned about that particular situation. I think they're only raising the issue now because the reality is it's the currency value that drives whether people shop in the United States. It's not the duty exemption that's driving cross-border shopping.
On May 31st, 2012. See this statement in context.