The dollar is stronger vs the yen than it was a few years back. That has been a factor.
Ever since I bought my first digital I have been watching Canon and there are always sales or deals.
At time they gave away top end printers as part of the deal, but that is just a way to sell expensive ink and paper.
Price drops also seem to come before a release. For instance the 1Ds III had substantial drops in price right before the release of the 1Dx.
The 5D II had drops right before the 5D III. If you notice the 1Dx is about 4.5k, at the same or less than the 1D IV was selling for at the release of the 1Dx.
So you have several things going on, the normal price cycle of the technology and the drop in value of the yen.

The L lens drops Joel mentions I believe are the result of the weak Yen.