How Do You Feel About...

Works of art being used as book covers. For example:

(which, if you don't know, is a painting by Van Gogh)

See, I'm kind of partial to this painting by Théodore Géricault (Head of a Drowned Man)

Not that I'm thinking about book covers or anything...

Is it "cheap" to use the work of a long-dead artist on a modern book? Copyright (at least the modern, legal version) isn't an issue, but is it unethical? Thoughts?