I think that if Clay hadn't been such a "geek" at the beginning of the show he would have won more fans earlier. Sorry, but I have to agree with Simon on this one. He did get more handsome as the competition wore on. I also think his consistency on some of the later shows cost him a little. Obviously it didn't take much, Ruben won by so little. By that point in the show it came down to switching loyalty, and Ruben had been consistent throughout the show. Clay was more diverse, but sometimes he didn't pull it off very well.
Of course, I also think the big reason was the comments of the judges. Face it, many Americans can't think for themselves, so when all the judges, but especially Simon, compliments Ruben week after week they listen. There were times when I noticed Ruben was pitchy or just not on par, yet they would still sing his praises. They were pretty hot and cold with Clay.