I know Wusthof know better, but I suspect that they suspect that consumers don't know better. Honing does make a blade "sharper", after all... if someone just knows that their knife is dull, they won't necessarily know that the thing they need is called a "honing steel", just that they want to make their knife sharper. Looking at Amazon search results, the same decision has been made pretty widely.
If you want to make very precise distinctions, "sharpening" is not a good word, because both honing and grinding make a blade sharper. ("Grinding" is not often used to describe what you do to a chef's knife with a finely-grained stone, but that's the most precise description.)
Oh, and just to make things even more confusing: The term "honing" is actually a little inaccurate too. "Honing" in the context of machining actually refers to a form of grinding. A honing/sharpening/whatever steel mostly works by burnishing and bending the edge back into shape.