The intended purpose of RSS is to distribute links and related metadata and not to actually distribute content.
Now, that said, there is a field named
description that allows for text to be stored. Normally, this is going to be a short description or summary of the content but not the actual content. A good example is Slashdot, which displays a summary and relevant links. A different take on the description field is to include the first sentence/paragraph of content, as used by Penny Arcade. And, finally, there are others that actually do distribute content through feeds, such as Ars Technica.
With Delicious, the description field is actually something that you specify when creating the bookmark. See the highlighted portion in the screenshot. So, if you have some way of capturing content when the bookmark is created, then you see the content in the feed. Of course, even if you do this, then the content may not necessarily be in sync with the original source.