Not entirely true. The sister plane to TWA 800 (both were 747-131's delivered to Iran in the early '70's), blew up in midair in 1976 over Madrid, Spain after (supposedly) being hit by lightning.
Never say never.
The 747 is great plane with a marvelous safety record but, did it ever occur to you tin foil hatters that the cover-up may be on the Boeing end of it?
Several Boeing 737s have suffered catastrophic accidental center fuel tank explosions as well.