Syndication feeds, by definition, consist of only the content. In fact it is not accurate to say it is "plain text" because actually it isn't: it is in feed format that happens to look like plain text if viewed with a browser. See

http://en.wikipedia.org/wiki/RSS_(file_format)#RSS_2.0

or

http://en.wikipedia.org/wiki/Atom_(standard)

for example.

EDIT: sorry but those links won't properly linkify themselves in here

Not sure if this is a 'solution' but I found a select box in my rss feed reader (Akregator) that gives me the option:
:
"Load the full website when reading articles"

I also note that if I choose to 'open in tab', that too renders as per the website layout. So perhaps it has something to do with the rendering in the reader again?