John - this looks like the scenario we postulated a few months ago with a lapdock going rogue - a Supply's Gone Wild video is the result!
Pretty amazing that D17 managed to desolder itself as that means the joints got North of 650 degrees F. That also means it went out-of-circuit and was therefore no longer providing over-voltage protection for some amount of time until the power was cut.
It's possible the phone charger does, indeed, supply 5.0 volts at 1200 ma, but its open-circuit voltage could be upwards of 6 volts or more, perhaps due to high internal resistance. If that's the case and the Pi is only drawing a few hundred ma due to the powered hub taking the load for peripherals, the semi-loaded phone charger could easily have been delivering closer to 6 volts, or more. A similar situation could have been occurring for the USB hub's power supply, and in the worst case where both supplies may have been delivering significant over-voltage, well, D17's days would have been numbered in any case.
I would look for something like a staple on the carpet that could have caused a short - all of the typical carpet materials should be insulators. Static wouldn't be a factor in this case, unless a discharge caused a semiconductor power component to go stupid at just the wrong time. A short shouldn't have resulted in D17 trying to commit suicide though, that still points to an over-voltage situation.
The best things in life aren't things ... but, a Pi comes pretty darned close!
"Education is not the filling of a pail, but the lighting of a fire." -- W.B. Yeats
In theory, theory & practice are the same - in practice, they aren't!!!