that doesn't really make any sense. as you said the NHL deals in US currency - regardless of how much the Canadian dollar fluctuates they still pay out the same amount in USD. actually if anything it would make more sense to have more canadian teams while our dollar is strong in relation to the US - every Canadian dollar made from ticket sales etc is actually worth more American dollars, bringing in more of the currency that they use. lets assume ticket prices remain relatively stagnant between seasons, throw out a # of $50 CDN for a ticket - at parity that translates to $50 USD, as opposed to what we used to be at around 70 cents which translates to $35 USD.
They avoided Jim Balsillie because they hate him from previous ownership attempts and they think he's a flake. It's actually more likely that they don't want another Ontario team because the market is very Leafs focussed (the Leafs are the richest team in the organization despite having their poor record). Your point about the salary costs makes a little sense to my line of reasoning though. They get a greater profit margin from the area having just the Leafs and Senators in Ontario - more along the lines of why they don't have another team in Ontario per se though, not why they supposedly intentionally have small market teams.