Moreover, in order to build out to 320, 640, or 1280 GB with SSD you need only off the shelf technologies (SATA/SAS raid), it's not even that expensive (even a 1TB top of the line SSD array in RAID 10 would cost less than $50k). To match that amount of storage in RAM would require multiple machines, rare motherboards or other hardware, and a huge outlay for RAM. Not to mention it would require pretty significant rewrites of their applications in order to use the RAM properly.