Don't let that board fool you. They often cancel Acela's during inclement weather because of traffic concerns (frozen switches causing limited routes). It has little to do with the actual equipment. Additionally, they are confined to certain routes, can not low level, can not be expanded and hog power. So, if you're looking to optimize your railroad, they'll send out the amfleets to serve the most passengers with fewer trains.
Makes a lot of sense. I somewhat assumed it wasn't due to technical issues as much as just an operational strategy.
I guess the OP question was originally a technical one (e.g. how well does the physical trainset do in these conditions), but ultimately it doesn't matter
why a train isn't operating. It just matters if it's yours or not!
Also, I imagine if "stuff" really hits the fan and you lose all electrical power it's easier to lash up a Diesel engine to a NER and move it than it is to do that with an Acela.