This would make micromorts very situation dependent which would diminish their value as a statistical tool.

Even an acitivity like driving a car is situation dependent. Careful drivers have a different risk than reckless ones. At the same time the table doesn't show you separate values.

This makes perfect sense in a model where the body is able to repair itself but the repair mechanisms can be overwhelmed with a sufficient stimulus.

I agree with that model, but I would point out that there are plenty of people out there who consider the bodies ability to heal itself from cancer pretty nonexistent.