This isn't an attack on cryptosystems, unless you torture the definition, so that SSL/HTTPS is no longer a "cryptosystem", but rather "SSL/HTTPS deployed on Dell Inspirons talking to IBM Blade servers running Apache".
As Spaff points out in the comments on Felten's blog, DRAM reminiscence isn't new.
As another commenter points out, stealing DRAM chips from wakeful computers is slightly outside the threat model for full-disk encryption. The purpose of full-disk encryption is so that Fortune 500 companies don't have to issue press releases every time someone loses a laptop. The new guidance to those companies may now be to disallow "sleep" mode until disk encryption systems get effective at zeroing keys before sleeping.
Problems like this are what motivates things like the Intel TPM.
As Spaff points out in the comments on Felten's blog, DRAM reminiscence isn't new.
As another commenter points out, stealing DRAM chips from wakeful computers is slightly outside the threat model for full-disk encryption. The purpose of full-disk encryption is so that Fortune 500 companies don't have to issue press releases every time someone loses a laptop. The new guidance to those companies may now be to disallow "sleep" mode until disk encryption systems get effective at zeroing keys before sleeping.
Problems like this are what motivates things like the Intel TPM.