There is a brief explanation of the reasons behind that (with links to further information) in the article:
> Yahoo! succeeds in Japan and Taiwan through its nearly two-decade-old partnership with Japanese SoftBank and its 2007 purchase of Wretch, a Taiwanese social networking site.
That makes it sound 50/50, but it's more diluted than that - Yahoo Inc. only owns 35.15% of Yahoo Japan. Softbank owns a little more - 35.86%. The rest is owned by much smaller shareholders.
SBBM is Softbank as well, so Softbank actually owns over 42% of Yahoo! Japan. In practice it's really Softbank's internet content and portal service in Japan that also leverages Yahoo! Inc. technology as needed as well as their brand.
I didn't see Taiwan on the map by the way, but yeah it's a joke amongst my Taiwanese friends that you're not a true Taiwanese unless your browser homepage is http://tw.yahoo.com/
> Yahoo! succeeds in Japan and Taiwan through its nearly two-decade-old partnership with Japanese SoftBank and its 2007 purchase of Wretch, a Taiwanese social networking site.