requesting URLs like http://en.wikipedia.org/w/index.php?title=Cat&action=history&feed=rss is an easy way of DOS-attacking a small MediaWiki website. These requests are quite heavy (diff generation for N revisions, with fetching all those revisions from DB?), have no captcha (because RSS readers don't support that), and since legitimate users almost never use them, they result in a cache miss.
Please make a configuration option to disable this "feature". $wgFeed is not good enough: RSS is quite useful for Recentchanges/Newpages, we don't want to disable those.