To me, cut along socioeconomic lines just didn't work as English in this context. I don't see cut along and cut across as being opposites. Cut along works when you have scissors and something with a line along which to cut it. I can't think of a simple construction that describes something you'd expect to be indisciminate affecting a town differently in a way that reflects unrelated characteristics of the town. Perhaps the flooding affected the town along socioeconomic lines. Bottom line, newspapers dispense with their subeditors at their peril.