Discussions on character encoding and glyph gaps in the CNS font can be found on Chinese Mac Google Groups

In other words, Hiragino Sans CNS is not simply "Hiragino Sans with Chinese characters added." It is a designed specifically for readers of Traditional Chinese (as used in Taiwan, Hong Kong, and Macau). The stroke shapes, character forms, and even spacing adhere to Taiwanese educational and governmental standards, not Japanese or Simplified Chinese norms.