The registry and system files are used for all sorts of things by drivers and the operating system. AND, drivers are only one way to get code to execute at ring-0. You can start kernel threads dynamically without using a driver. You can patch physical memory. You can interact with any 'object' such as shared memory sections, device objects, cache blobs, and memory mapped files.
Security is an illusion.
It's really just called 'risk management'. If you are not involved at boot-time, you have already lost. I haven't looked at the IPD sources, but based on their description, it is clear that it would help. Unlike you, I didn't read that they claimed that IPD would restore an untrusted system to trusted state. One of the problems with loadable kernel drivers, or any loadable ring 0 code, is that it they are loadable.