I think that most trees in cool regions get the majority of their good
photo-synthesizing done in the first few months of leaf growth. Leaves are
constantly being attacked by insects and pathogens, and I'm sure that the
methods that the tree uses to retain them (harden them, add more harsh
chemicals to them, etc) interfere with the straightforward process of
turning sunlight into food. I imagine that most northern trees can survive
just fine if they get 3 or 4 good months of good photo-synthesis in with
nice juicy green absorbent leaves, and if they are just dropping their
leaves now, in early August, that means they had April, May, June, and July
to make food. I think trouble is more guaranteed when you get several
adverse events several years in a row. (Drought one year, insect infestation
another, very late frost one year, very early frost another, too much rain
another). I think the East has gone from one or two years or rather severe
droughts to a summer with too much rain in many places. The trees might be
reacting to yet another stress. I wouldn't write them off until you've had
one or two "normal" years, to see how they do when conditions are actually
favorable for a switch.