Well I have to say if you cause a fire you would have to be pretty careless with your things. Steam is a digital service so anything at anytime could happen to Valve/Steam and anything at anytime could happen to your games that you downloaded. Also since they are all digital based games they will not be there forever and neither will Steam. At least with a physical copy, it's there and you won't have to worry about anything as long as you are a responsible person and careful with your games.
But I guess nowadays people don't want that heavy burden called "responsibility". I seriously think this digital age stuff is making people so lazy anymore. It may be very convenient but its also making people so careless and lazy anymore because with downloading you just download it and forget about it not thinking of the consequences. Some people just think since it's downloadd I don't have to worry about anything anymore it'll always be there when in fact for Steam's case it won't.