There has been a huge "asic rush" in the last days because several miners have become "available". Many meople might have moved their coins into buying some of those miners or a share in a "mining company".
If you look at the "custom hardware" section of the miners forum, you will see what is left of this "asic rush". Most of the group buys are over and people are back into market again.
but this is only a theory!
Not a bad theory, I wonder if and what connection is there between the PRISM expose to this drop