Of course they would charge everything else including used guns, key chain, or stickers. Why would they deal with the exchange headache that might end up costing them money? Let customers deal with it. All other Canadian dealers and distributors deal with items in USD and convert them to CAD so that customers don't need to deal with exchange rates and can give their customers exact price and cost before ordering.
IRG get their inventories in USD, get paid from customers in USD, and save their profit in USD. What's not to like? All works out well for IRG.