Dan never ceases to impress me...
I consider myself to be "somewhat" of an authority on maple trees and our "fave", the whitetail- especially in regard to the sugar maple as a browse species for deer. I have watched deer interact with maple as a species for decades. Last month I sold my property that contained tens of thousands of sugar maples and I hunted it a lot. I have watched what the deer do in this environment over and over for many years.
The starch content of maple leaves is highest in early fall. When they fall off the tree the deer absolutely love them. The starch is leached from the leaves when they turn brown and deteriorate. As far as being a sweet treat for the deer, those first couple of weeks are primetime.
What most hunters do not realize is that maple leaves, especially the sugar maple, contain surprisingly high levels (much higher than most other leaf types) of magnesium, calcium and potassium
WHEN THE LEAVES FALL FROM THE TREES. This double-whammy of high sugar and mineral content is very attractive to the whitetail. As several of you have mentioned, the deer are all about it.
High mineral content alone is a draw for deer in leaves, and why they love stripping the leaves off of dogwood trees spring / summer and fall.
Back to the maple, the deer will eat these leaves whenever they are available for browse, even when the starch and mineral content is lower. There aren't always a lot of young maple around and when the mature trees drop leaves by the thousands in fall the deer can eat them with little effort.
Another observation of the whitetail I have made that I really haven't read anything about is the deer eating "brown and down" maple leaves. Many, many times I have observed deer eating maple leaves that have been down for a long time and they have become brown and crunchy. They are not nearly as preferred as they are at leafdrop, but I can't help but shake my head when they do this. I reason that the starches have likely been leached from the leaves, but the minerals remain.
Yes, you heard it right and that's what I said... deer of all ages eating brown and crunchy maple leaves.