It really does. BMW-engines consist of an aluminum-magnesium alloy. Once the engince catches fire (engine overheat or spilled fuel by a broken fuel pipe)there is almost no way to fight it.
The radial engines of the Convair420/440 consisted of aluminum-magnesium, too. With an engine fire (causing dense white smoke) you better prepare for a parachute landing.
Fire extinguishers will fail fighting a magnesium fire and water makes the flames higher.
The only way of extinguishing the fire is letting it starve by lack of oxygen.
Well, thing of it this way, if any part of the engine survives the crash you can use a sharp knife to scrap a block of what's left of the engine to make a fire starter =P Just add a little bit of iron oxide and you can't even starve it for oxygen =)