Here's a passage from Wikipedia on BitLocker
Once a BitLocker-protected machine is running, its keys are stored in memory where they may be susceptible to attack by a process that is able to access physical memory, for example, through a 1394 DMA channel. Any cryptographic material in memory is at risk from this attack, which therefore, is not specific to BitLocker.
It is my understanding that Trusted Platform Modules (TPMs), which BitLocker is allegedly using are made to specifically protect against such attacks:
... a key would still be vulnerable while a software application that has obtained it from the TPM is using it to perform encryption/decryption operations, as has been illustrated in the case of a cold boot attack. This problem is eliminated if key(s) used in the TPM are not accessible on a bus or to external programs and all encryption/decryption is done in the TPM
TPM diagram implies that key storage and encryption/decryption engine should be part of module. So, why is there no full disk encryption product, which uses this feature? E.g.: why is there no FDE software, not vulnerable to cold boot attacks?