Finallyme,
I see two differences with the Ti Jetboil:

1) The Ti is less conductive so more heat will build-up at the base of the pot.

2) The Al heat exchanger has a different thermal expansion than the Ti pot so every time the pot is heated up and cooled down it puts stress where the two are joined together.

I am guessing in these failures the heat exchanger breaks free from the pot. As a result the aluminum is not being cooled by the water in the pot and begins to get much hotter.

Also, having put blowtorches on aluminum before, I am guessing the heat exchanger is not melting but is burning away. I would be surprised if you get globs of molten aluminum.

The explosion warning comes from the excess heat building up and warming the gas in the tank. This will increase tank pressure which could cause the tank to rupture. If that happens you have high pressure/temperature fuel, air, and flame... that equals explosion. I am not sure what the actual explosion risk is. Since you would probably get a similar result by running the Jetboil dry, I would guess they designed the system to withstand such an event without exploding.