We have a 100+ year old white oak that seems to be thinning or at least the leaves have gotten smaller the past two years.....can this be corrected with feedings? Is it attributed to the two hot summers and the really bad winter this last year?

You have dialed in the answer pretty well. The drought of 2012 and a not so good summer of 2013 coupled with the severe winter have all contributed to the trees health. Leaf size is a good indicator of tree health. A thinned canopy could also be he result of bud and twig death caused by the cold winter temperatures. I am sure an arborist would suggest a plan to return the tree to better health would include feeding, possible canopy thinning to balance the root to shoot ratio and regular water on your part as a way to improve the situation.