Anna Wintour, famed editor-in-chief of Vogue US, has never explicitly said that she refuses to put models on the cover of Vogue. She has noted in the past that celebrities on the cover self significantly more copies than models on the cover (2012's worst-selling Vogue was covered by Ryan Lochte, Serena Williams, and Hope Solo, so it's possible athletes need to be added to that formula as well). Alexandra Shulman, Vogue UK's editor, featured four models on the cover this year; Wintour hasn't had a single one since Kate Moss in September 2011.
Karlie Kloss's 2012 achievements actually exceed those that I could fit into the panel. Most notably, she was the centre of at least two Photoshopping scandals (one to remove her visible ribcage, the other apparently to give her a third armpit), shot a TV ad for Target's Holiday sale (and reportedly brought desserts for the crew), wrote a recipe for a fashion-related cookbook, and managed to find herself at the heart of racism dispute following her appearance in a Native American-inspired outfit for the Victoria's Secret fashion show. Somehow she also found time to be romantically linked - in the tabloids, at least - to actor Eddie Redmayne, St. Louis Rams quarterback Sam Bradford, pop-muppet Joe Jonas, and investor/Trump-in-law Joshua Kushner.
Ah, for the energy and work ethic of a 20 year-old!