All such lists just remind us what the effect of a mainstream sport is.
Remember when we had the "sportsman/woman of the year 2010" posts in here? You had no cyclists up in the top 20 at all. Sebastian Vettel made it to #4 despite squeaking over the line to the title in F1; in the women's list you had a wider range of sports, but quality of achievement played second fiddle to the mainstream appeal of your sport; as I self-righteously complained at the time, Lindsay Vonn was placed at #2 but Magdalena Neuner, who got more medals, more gold medals and won the World Cup that year, wasn't even in the top 20.
But then, in minority sports, just being HEARD OF makes you bigger than anybody else. Ole Einar Bjørndalen made it to the top 10, despite being roundly out-performed all year in 2010 by Emil Hegle Svendsen. But Bjørndalen's longevity and success level has meant that for many people he's the only XC/biathlete they could name, and so he's the one that gets mentioned.
Maybe if Cavendish has another three or four years of success at the same level people will take him to heart. But I doubt it. There's only the one gold available to him at the Olympics (assuming he won't try the Madison again), and like it or not, the Tour de France supercedes all else. And while Cav may be more marketable than a GC contender who buries themselves in the bunch and gets placements, like a Levi Leipheimer or Jürgen van den Broeck, he isn't going to be more marketable than the winner, because people who don't know the sport will only look at the winners OUTRIGHT. They don't know or care that there are 21 individual races and Cavendish is winning 5 of them, they just know that he's 150th at the end of it.
You want a quick sale? "My guy won the Tour". If you want a quick sale, you don't want to have to explain why what your guy did is so incredible. You need them to be winning at the biggest events. An Olympic gold medal or a yellow jersey is something tangible; everybody knows what these are. The green jersey? Not so much.
Well, that and appearance counts. Let's not make any bones about it. Let's call it Kournikova syndrome. A footballer like Ronaldinho can advertise sporting products - everybody recognises him as a great footballer. A footballer like Thierry Henry, however, he can advertise a lot more; he's photogenic, he looks good. Calvin Klein doesn't want a guy looking like Ronaldinho in their adverts. But a guy like Federer, Henry, and so on? Sure. Hence why Lindsey Vonn was 2nd in that list of athletes of the year, and Maria Riesch, who achieved more than her in 2010, was only 7th.