RE: Helped plant 300 "cordon fruit trees" today!
It's the way you prune them in combination with the angled planting. I guess in Europe some folks will plant them that way to serve as a sort of fence (hence "cordon"), especially around gardens, because other folks can't accidentally wander through trees leaning like that. But they have to be pruned a certain way or they'll just grow into leaning regular fruit trees--those articles I linked describe how to do it. My neighbor bought dwarf varieties so they'd be even shorter, but I think you can do it with regular versions.
We get such terrible blustery days here, especially throughout the spring, and the wind always comes from the west, so I'm thinking (for us) using this method and leaning the trees toward the east might actually minimize wind damage. Less canopy to catch the wind, and less stress on the tree trying to stand upright against the force.