Prices depend on Canon's inventory levels. They have sales when inventory is too high. They like to keep their factories running at their best efficiency.
We do not have any details about lens inventory, but its a safe bet, given the world economy that there is a surplus.
I expect another sale soon, but went ahead and bought a 24-70mm LMK II at the last minute
One thing to consider is that May and June are the best selling months (other than big sales at Christmas). People planning vacations, wedding photographers, etc buy them in the late spring. If inventory is low, there will be no sales.
You could also read the CR post. http://www.canonrumors.com/forum/index.php?topic=13883.0