Most secure chips are used as the root of trust for the rest of the system. For example, to implement a secure boot process. If a secure chip was replaced, the system wouldn't boot up (since the security key required for secure boot is missing).
What a great idea - special secured chips from the same fab who make the counterfeits.
The nonsense of all this is the management of the security.
Say my US distribution company were to pull apart the unit, pop the "secure" chip off the PCB and replace it with the same one someone-else had programmed, put the unit back together, and on-sell/deliver. Who would find out ? No-one.
Even if the chip were programmed to frequently broadcast its "secured" status. Who would listen ? What would they do about it ? Stop the launch, hold the plane, not fire the missile, switch off the pacemaker ? How easy would it be to spoof or obsfucate such a status message ?
The real issue is not the reconfigurable silicon, but rather the programming tools. How do I know if my/contract tools are not compromised with some nasty little timer ?
Sure, the chipmakers say every little intrinsic security improvement is helpful. Is it, or is it just window-dressing to distract us from a more likely reality ?