The law basically says that if a wild land fire starts on your property, you're responsible for the damage that others suffer, and if you were negligent in allowing it to start or in failing to suppress it, you're liable for the costs incurred by others to do so. It isn't worth the costs associated with going after a 19 year old kid on a dirt bike,with a minimum wage job, but certainly, anyone with major assets, like a railroad company, or a homeowner with liability coverage, is worth the trouble. Otherwise, the taxpayers collectively eat the failure to behave in a responsible manner. Defensible space works even in the "big one". I've seen 50,000 acre plus fires that devastated entire drainages, except the properly prepared homes.