All makes perfect sense regarding PMA turbine blades. I hadn't considered the differences in through-blade cooling airflow - very much a critical concern in that part of the engine core. Thank you LomaP and TD.
I thought GE re-jiggered manufacturing and overhaul specs after the first couple of HPT disk failures and those changes were designed to mitigate these events - but my point may be moot as we really don't know what happened yet.