Thanks for that link...this tree thing is a bit overwhelming in that there's so much to learn.
Don't know about the dogwood, since it was here when we bought the place, but we planted the Japanese maple five years ago and the only physical damage I can think of could have been caused by my cat scratching it (?). Other than that, no weed whacker or mower has been close to it.
Hmmm...maybe ice falling off the roof? The drip-edge is pretty much overhead, and a couple of winters ago the ice dams were over eight inches thick...
The ice theory still stands because the slabs came down through the branches when friend well-meaningly shovelled our roof. Chunks were five and six inches thick, and indeed took off some branches as they thundered down.
As for deer, we don't have many down here for some reason. I mean, they're around but I only see them maybe once a year in the woods, and this tree is only four feet from the house.