Think of the PCR enforcement as a signature check on your running OS at the time the secret is released. I think its hard to claim there's no value in that. Some will argue that the binding between PCR state and OS state is too weak - you can potentially replay an event log to put PCRs into a known state - and that's a valid criticism. But there are a lot of trade offs here in terms of other types signature checks vs using a TPM.

I've been blogging about some of these issues over here: https://www.ibm.com/developerworks/community/blogs/smartersecurity

Kent