I was taught to paint by instructors, and then refined my abilities by studying paintings of the old masters, right down to their brushwork and core techniques visible in the paintings to all who see them. Now I go and create a painting called Sunflowers. Does Van Gogh's estate own some of my work?
No one is necessarily saying that you owe Van Gogh a cut. What they _are_ saying is not to claim that you didn't train on Van Gogh or to pretend that you don't know what you practiced on.
Should every HN comment I write include a full list of everything I've ever read? What about a commercial work like a book, should that include a list of everything I've read or heard in the past 35 years of my life? That's a lot of attribution to keep track of ...
edit: I guess my question is where does derivativity end and creativity begin?