By which you mean "cars catch fire all the time when they crash".

http://www.chandlerlawgroup.com/library/national-vehicle-fir...

(stats from NFPA).

Fuel tanks don't catch fire if you shoot at them with tracer bullets (see the old episode of mythbusters), why should they explode when the car hit a tree? It was a nice car, well designed, and surely the engineers at BMW had considered various crash situations, including a front colliosion with a blunt object.