for instance Johann Wolfgang von Goethe: https://de.wikisource.org/wiki/Johann_Wolfgang_von_Goethe#Bibliographien
Goethe was an author, but there are also works about Goethe. In de.ws portal-page and author-page about Geothe are merged in one. There is no difference. Don't expect something else.
Well, that's something that every Wikisource cando: adding books *about* an author in his Author page. It.ws does this too.
BTW, Italian Wikisource decided for a Opera namespace because we just find it very useful to differentiate with "normal" books in ns0. It's just more clear for us, especially regarding Wikidata integration.