It's because as the writer of the article mentioned, plants/trees grow roots even after the foliage dies down until the ground freezes, and their root growth stirs and starts a lot earlier deep down even when the surface ground is still frozen in late winter/early spring, before you can even begin to think about digging a hole. (in fact, some people say you should dig the holes for planting in spring in previous fall and keep a supply of unfrozen soil to fill with -- but I've no idea how to do that without having the tree to eye-ball the hole size with
There are some species more suited to fall planting, and there are some that shouldn't be planted in fall where the winter temps are severe.
But I'm pretty sure fall planted apples do very well, even before frost if potted or B&B, or bareroot and dormant after frost and light freeze.
Its a good idea to put a plastic or metal trunk guard and put up a fence to protect from mice/rabbit/deer munching on them, and mulch well to protect from soil heaving due to freeze thaw cycles.