Supposedly a fire at one of the factories that manufactured the chips caused the supply to drop. Supply drops and demand remained the same and/or increases equals higher prices.
Similar thing happened with harddrives not long ago when flooding at one of the factories caused the demand to be higher than the supply and thus hard drive prices sky rocketed. They are just now getting to a pre flood price.
I read somewhere probably mid last year, that the rise in demand for DRAM by the mobile devices industry (smartphones, tablets) pushed much of the manufacturing facilities to prioritize manufacturing for those devices, lowering the supply for desktop modules, especially for system builders like us.