We have been asked to ignore the possibility to consider this thread as flamebait, so...
The main problem lay in the fact that the 2 contenders are the (almost) nationalistic France, and the almighty, untouchable USA....
No, wait, the contenders are 2 airlines company, an aircraft producer, and a judge, correct?
Pick your choise.
IMHO, the main responsability lay decisively (sp?) in the Air France that decided to accept the risk, instead to adopt a probably difficult solution (weight, balance, cost), for a known potential danger, and partially in the Concorde builders.
Anyway, as tronsky pointed, such potential dangers are commonly accepted "under the desk".
OTOH, it's supposed that an arcraft dont loose pieces (IIRC it even happened before).
Resuming:
I'll hold Air France greatly responsible, knowing the problem, and not having a team inspecting the RWY before each take off.
Concorde constructors can be held responsible only if they have stated somewhere in the operative specs that the concorde can operate from non standard RWYs.
The Airport share with AirFrance the part of rersponsability to not having controlled the RWY, 7/7 24/24.
Even Continental have it's share, but only if such parts losing as happened before (why use a stronger component? it broke before?), and/or if the crew realized that the part had detached and did'nt informed the tower.
The DC10 constructor may have the same kind of responsability as the Concorde constructor, but, again, only if this part has in other cases showed this nasty tendence to fell off.