The prices of Canon lenses and dSLRs do not just follow the exchange rate trends. They depend on them, of course, but it is not that simple. Canon has is doing business in the USA as well, it is not like they have a factory somewhere in Japan, and price their equipment in yen. In the lest 7-9 years, the yen has been as low as 123 per USD, and as high as 75. The prices did not follow that wild ride. BTW, the prices of P&S went down.
Now, the yen is at its 2008-2009 levels. Do not expect the prices to go that low.