User blog comment:El Alamein/Braxas vs. Smaug/@comment-4098900-20120831000516/@comment-143604-20120902025507

I remember watching a pretty awesome special on Animal Planet back in the day, and while obviously HIGHLY speculatory, it mentioned the concept of a sack being contained inside the dragon which creates the flammable material used up to cause the dragon to breath fire. I would imagine that a larger sized dragon would have a larger whatever-fire-organ, and thus be capable of more generation of fire. I'd assume that's the line of logic being went with here.