As someone who has written and maintained an RSS aggregator for years, I can tell you that this jankiness is in big part because of how vague and under-defined the feed formats (RDF, RSS2, Atom) are, and how "creative" various websites are in producing feeds which are just barely standard-compliant, but also just enough screwed up to cause problems when parsing them.

It was a headache after a headache trying to get all the weird corner cases handled.