The significance is that all of these as well as most other text forms that must be parsed efficiently only recognize ASCII whitespace lexically, even when they recognize Unicode for data. The only exception I found was ECMAScript, which accepts a broader set of whitespace lexically, but still not full the Unicode – I’ll bet that was a performance choice as well.
There is nothing to gain by supporting other forms of whitespace lexically. It isn’t an internationalization issue. Unicode needs to be supported for content, not markup.