Well, the price increases must be due to something. The "yen to dollars" thing so often quoted is no excuse either, because Nikon is equally (or if anything more) purely Japanese as Canon, and they seem just a bit cheaper as I see it. But of course they don't really compete directly in the ordinary sense of the word, because their lenses are not interchangable.
Right, and if you priced out comparable setups, Canon doesn't look so bad unless you were planning to use a $200- zoom on a $3000 body. The Nikon glass is generally more expensive. While the whiners have been whining about the latest Canon bodies, Canon has been quietly updating already first rate glass.
The exchange rate drives costs. Prices are driven by supply and demand, which is influenced but not directly related to costs. But increased costs do need to be absorbed somehow -- either through higher prices on the bodies, the glass, more sales on those, or more revenue through other channels. Otherwise it comes out of profits, but if too much comes out of profits, they become losses (e.g. Sony), and if the company lose too much, they eventually go out of business (Kodak, Pentax, etc)
I think you've got this kind of back to front -- it's not that Canon are abruptly becoming expensive, it's that Nikon are using aggressive pricing on their new bodies to increase their market share (at the expense of Canon). They are probably counting on their D800 buyers to also go out and buy (for example) their 24-70 and 70-200 lenses (which are more expensive than the Canon versions)