Well, if exploding Boeing center fuel tanks are such a common occurrence, shouldn't we issue an Emergency Airworthiness Directive? The FAA didn't exactly press hard for fuel tank inerting after this crash, and they've just dabbled a little with the technology, even though it would be fairly simple to do.
By comparison, a lot more interest has been shown in missile countermeasure systems, and several companies are pressing ahead with systems, despite the massive cost and problems the systems pose.
One of the issues is the volatility of jet fuel in general. According to the NTSB's own data, the highest possible temperature in the center wing tank is just barely over that at which Jet A releases flammable vapor. Still, this mixture is only capable of deflagration, not detonation. The temperature required to create an explosive mixture from jet fuel is unobtainable outside of the engine.
Looking at the evidence available in this case, you have to come to the conclusion that a missile attack is at least possible, if not probable. Over 180 eyewitnesses on the ground described a classic MANPADS engagement- a streak of light that rose from the ground and exploded in an initial white flash before the fuel ignition (one witness who was a military veteran is adamant that it was ordnance, as he'd seen it before).
Add to that the rocket propellant traces in the cabin, the radar evidence, the terrorist warnings THE DAY BEFORE and the day after, the FDR anomalies, the structure damage anomalies, the debris field with all CWT pieces found together, the impossibilities in the NTSB explanation, the CIA animation explaining what we actually saw, reports of 1/4" metallic pellets in some of the bodies that are identical to those in missile warheads, the constantly changing story from the FBI and NTSB in the first few days, the numerous slips of the tongue from politicians during press conferences and interviews, etc, etc, etc, etc.
I think it still remains a possibility that the CWT exploded for undetermined reasons, but after considering all evidence that is known, the missile theory is the most likely. The only conspiracy here is the reasons for the government covering it up, and if it was justified, and if it is still justified.