Because Yuna and Ando aren't main rivals. Yuna and Mao have been competing against each other since juniors. Yuna and Mao are mentioned in the same breath most times, in that, when you talk about Yuna, you don't compare her to Ando, you compare her to Mao, and vice-versa. Kwan's main rival was never Butyrskaya, even though Maria beat her at Worlds. Slutskaya was the one. Sarah Hughes beat Irina, Michelle, and Sasha in at SLC. However, I wouldn't rate Sarah Hughes as a main rival of Kwan as I would Sasha or Irina or Tara. Carolina is similar to Maria in that respect. As was Joannie. They may beat one, or both, of Mao-Yuna, but they're not rivals.
Again, I'm sure at the top that everyone is a rival, at least a little bit, because you are going up against everyone. However, one way to KNOW who someone's chief rival is, is by asking their fans. Ask MOST ANY Yuna or Mao fan "Who is your skater's Chief Rival?" 9 out of 10 times, they'll say the other. Jeremy Abbott beat both Johnny and Evan multiple times in 2008, 2009, and 2010, but if you ask Johnny and Evan fans "Who was Johnny/Evan's Chief Rival: Jeremy or Evan/Johnny?" 9 out of 10 times, they'll say Evan/Johnny.
As for Yuna's 2010 Worlds performance, it was extremely predictable. The Worlds after an Olympic Games tend to be unpredictable, in that: people retire, people don't go, and the skaters who do go have endured a VERY long, and stressful season (especially for the OGM and other medalists) and there tends to be a mental and physical letdown, as they AREN'T building towards Worlds like a usual year, but to the Oly Games.
Also, I understand what you were saying Jammers about how "that's the only way Mao could beat Yuna." However, you must understand that even if you may not have meant it in a negative way, it was taken negatively. The ice is slippery, and Mao produced, Yuna did not. Mao won, and she deserved to win, because Yuna did not perform. Similarly, we can all realize that Miki Ando took advantage of years where Mao and Yuna made mistakes, weren't competing, or were having down years. However, Miki DID take advantage, and full credit to her, she earned her World Titles fair and square. The ISU doesn't award World Titles with asterisks, and neither should we.