Not theory, fact. See also the comment below about apartments and roaches. Look at pictures of a major fire like Oakland Hills several years ago, and you'll see not all of the houses burned. Look carefully and you'll see that all of the survivors had a minimum of vegetation around the house, and perhaps more importantly, were of fire resistant construction. Anyone that staples kindling to their roof (cedar shakes) should expect their house to burn. Ditto big decks, wood siding, etc.