They should simply take the GUID instead of the content of the link tag. After all, the GUID in radio blog postings is always the link to the article itself (that's how it's defined anyway - only if the GUID element is marked with isPermalink="false" is it not the case). The Python Desktop Server does it exactly the same way, the link element contains the link of the posting, the link to the posting is in the GUID. So it's more of a problem with NetNewswire, that it doesn't ask the user which link it should pass as the link to the blog posting ...
At Der Schockwellenreiter there's the original article.