Interesting point.
I am not a professional plumber, but I know my way around mapp gas, solder and a torch.
I have wondered if it would be worth the peace of mind to put a few sprinker heads in the garage as a precaution. I am sure it would not meet "code" but it just could prevent a fire from spreading. Even if done with copper tubing as opposed to galvanized pipe, it would help. Water damage could be great, but considering the consequences, it might be worth it.
Any thoughts?