If you excerpt an article you're not supposed to post more of it in comments.
I do the [snip] thing in excerpted articles so that the pertinent parts of the article can be discussed, while bypassing a lot of blah, blah blah.
If you don't post the interesting parts of the article other people might do it so that they can comment on it.
If they comment on sections of the article that are not posted it doesn't make sense to someone just reading the post and not going to the source to read the full article.
[snips] are our friends.