@jcj: The system is not intended to be of the level of complexity required to determine "bad" inputs from "good" ones. The whole ethos of the Alternate Law system is to give the pilot as much control as possible while keeping as many systems online as it can. The A320 appears to have a limit on trim travel in Alternate Law, but - possibly as a result of press/professional backlash at maintaining authority, the A330's THS system gives the pilot complete authority at all times. One can't have it both ways.
@Winnerhofer: Perpignan isn't really comparable - in that case the AoA vanes failed due to water ingress from improper cleaning methods, which froze at altitude. The acceptance pilots also broke from the specified procedure when testing the safety features. In the case of AF447, every component in a technical sense (bar the problematic pitot tubes) was working correctly.