All kudos to Sully and his colleague by the way. Without the APU the aircraft would have flown in direct law, (just like a 737). Airbus aircraft land in direct law quite regularly after some in-flight computer failure so I’m sure Sully would have been able to ditch without a working APU. The argument that the accident report tries to make is a bit of a circle reduction. Yes the APU allowed normal law to protect the aircraft from stalling, but without the APU, Sully would have flown the aircraft in direct law, respecting the stall warning like in a conventional aircraft. He could have arguable made a more controlled ditching in stead of (unknowingly!) pulling so far back fully on the side stick that the computers had to take over to safe the aircraft from a stall over the Hudson.
The only area where the APU might have been critical is if an engine in-flight restart would have been possible. Which was not.
So more to the point, did the FAA change any MMEL after this incident regarding serviceable APU? Was there a need?