Freezing RAM to get at encryption keys has gone from "in the realm of elite law enforcement operations" to "standard procedure for many law enforcement units". Particularly in organized CP distribution cases, they have come to recognize the importance of getting the RAM while it is still on (and freezing it as soon as possible after gaining access to it). Although plenty of LE will still power down machines during raids, you really shouldn't count on them doing this these days, particularly if you are raided by the feds and they have any experience with people using encryption.