Structured comments solve a non-problem; Extracting useful documentation directly from the source code is useless if there isn't any useful documentation directly in the source code.
There are a large number of nearly empty javadoc and doxygens published on the Internet. Worthless documentation isn't better than no-documentation. At least with the latter it's harder to delude yourself into thinking you've got something. That means autodocumentation tools are simply making things worse.
Good documentation, means prose, not property lists on program definitions. XML simply doesn't enter into it.