PJ2
As an aside, while the US Airways flight will have had "Alpha-prot", (stall protection), the fbw system would not have protected this airplane from stalling in this case because the engines were incapable of delivering TOGA (Takeoff/Go Around) power. In "Alpha-prot", the airplane is not pitched down to reduce the AoA - the only airplane response is to increase power, so Captain Sullenberger had to fly the speed indicated on the PFD, (Primary Flight Display) just above the alpha-max stall speed and by the initial indications
Sorry, but there is a rat here :
On the 320, "Alpha prot" is just an AoA protection : between "prot" and "max", the side stick commands alpha directly. However, the angle of attack will not exceed alpha max even if the pilot pulls the stick all the way back. If the pilot releases the stick, the airplane will return to alpha prot and stay there. That,regardless of the thrust you have available.
On the other hand,
Alpha floor is the protection which is triggered with a high AoA and the airplane would go into a TOGA mode.
With the obvious lack of thrust, the system stays in AoA protection mode.
That's in all probability what happened to US 1549 as one of the NTSB press conferences mentioned that at their point of ditching, they were two knots below "prot" speed and just five knots above "alpha max" speed for their configuration.