When you think about what is natural it is natural to have the anchor text in your navigation menu the same throughout the site. It is NOT natural that everyone who links to you would use the same anchor text.
But it is also natural to vary the anchor text in internal links. I often link to the same story on my site when referencing it. Depending on the reasons for referencing it, I often use different anchor text. It is the most natural thing in the world.
Sometimes I might link to the "red widgets story" at other times I might link to "that great article on widgets". Are Google going to give me a hard time about that? Seems odd.