^I don't think there are as many 12 year old girls with a free flow of cash in the US as there are citizens of Japan or Taiwan. xD I'm not too sure about Jolin Tsai, but I'd imagine Utada to be on that list. She was on par with Ayu in all the Japanese articles about who pays the most taxes up until a few years ago... and she's got the biggest selling album in Japanese history.
With Ayu not being mentioned in the articles (and I'd believe it if she was cause it's Forbes), I'd say Ayu was never part of this article and it was only conducted on artists popular in the US (because the US always disregards things that aren't popular there.) Then someone saw the list, figured if they included Asian artists, Ayu would definitely have been in there (which she would've) and then posted it online.
