There is no doubt in my mind that a lot of this is arson. By who and for what reason is yet to be seen, if ever.
But with the construction industry in such a slump this is sure to put a lot of home builders back to work.
There was at least one instance that I heard about where a home suddenly burst into flames on the La Jolla Indian reservation. I guess it was miles from the nearest fire but has now caused a lot of damage to the area. I think the authorities will be looking into that guys finances to help figure that one out.
Stay safe.