6  BIS Review 30/2008  differentials between countries do matter to exchange rates, along with expectations about how those differentials may change (a function of growth expectations), factors affecting trade positions (such as commodity prices in our case), investor risk preferences and so on.
I have already discussed the case of petrol, but there is surely little doubt that the prices of tradable goods and services generally are lower today than they would have been if the exchange rate had been at its long run average level.