excuse me sir, when you save a document as SVG or PDF, you also save them in a vector format... but you don't expect the bitmap images to be converted to vectors.
personally, i don't suggest to open the PDFs with file > open.
and i'd really like Scribus to only open .sla files.
it's just a psychological / philosophical thing.
scribus can import and export pdfs.
and that's good.
but it should only be able to open and save .sla files (at least as long it loses information when importing and converting to pdf).
sadly, the team does not agree with me and too many people are deceived by the results, because they then think that scribus is a pdf editor. which is clearly not true. (even if you can edit PDFs at some extent).
rant finished.
now i will be able to sleep well : - )