It's actually the opposite of bowing, ODO, where the edges curl up and the center is concave. Here are some images. It can be to varying degrees. I've seen it in charming old places, now that I know what it is, and it looks rather natural with the old patinas and environment. It just looks like an old floor. My parent's house has a bit of it and the floor looks fine overall. There's a place around here that has a beautiful new vintage style kitchen with newer solid oiled flooring that has some mild seasonal cupping going on. It's still a beautiful room with a beautiful floor. If I hadn't learned about cupping recently, I probably wouldn't have paid any attention to it. It just seemed like an old floor and added to the older feel of the kitchen.
In these cases with the new pristine furniture finish floors and modern surroundings, it just looks defective, of course, and is extreme. I think the high gloss accentuates it, too.