Rob,
Doesn't surprise me much. If your car is involved in a contamination incident, even though it probably won't have any damage it will cost a fortune to have a hazmat team clean it up, which is why the insurance companies are excluding that.
Consider that there was a teenager a few years back that thought it would be really cool to get the glowing substance out of a tritium exit sign he found at a renovation site. Took it home and broke open the tubes (which promptly stopped glowing). He noticed the small rad label on the sign, and fessed up to his parents, who notified authorities. I think the cleanup of the house cost in the neighborhood of $250,000. And that was for something relatively harmless.
If your car is damaged in a nuclear blast, you probably have other things to worry about at the moment. <img src="images/graemlins/grin.gif" alt="" />
My advice is that if your car gets contaminated (depending on what with), just take it to the car wash and forget about it. Maybe run it through a couple times...
Or get a rider for your policy... <img src="images/graemlins/smirk.gif" alt="" />
Greg