Well Mick, the state of Ohio just made it mandatory to have auto insurance about ten years ago. Even then you only need to have liabilty insurance for damages caused by you.(the insured)
That's all these people (that hit the cow) had, they had no coverage for personnel liabilty. They were trying to sue the insurance company claiming that the cow was a uninsured motor vehicle, the company would then have to cover the damages under state law. However the court ruled that the cow is NOT a motor vehicle, therefore the insurance company does not have to pay. If they had additional coverage then they may have been covered, depends on the plan they bought.
They can still sue the owner of the cow in civil court.
I live in the same county (about 5 miles from the courthouse) so we've been kinda following this for a couple a days now.
The sad thing is, The insuance company will more then likely pay for the cow as the damage was caused by them(the insured).
EDIT:"What if they had hit a tree?"
Any damage to the tree would have been covered. Damage to themselves or the vehicle would not have benn covered.