My definitions:
- Static rollover is when center of mass is not over the footprint.
- Dynamic rollover is whenever other forces are involved.
I like Nick's use of "typical dynamic rollover", presuming it referes to dynamic rollover on a slope when you aren't at a static rollover condition. I think the universal probability he referred to considers only the "typical".
Rigid or articulated heads are just as susceptible to stuck skids/wheels, strong wind gusts, ground contact during lateral translation, etc. Of course, with cyclic control power always available they are more able to recover.
Matthew.