I've been searching around and I have not found the answer... I have read that the WordPress RSS Feed should display an Updated Post if you change the title or change the publish date, but it is not doing so. I have tried all sorts of different things - changing the date, changing the title, unpublishing and then publishing the post ... Nothing will consistently get the post to the top of the RSS Feed.
I use Feedburner, but that doesn't seem to be problem. Even when you put the WordPress feed ( http://www.chicagohotblog.com/feed ) into an RSS Reader, it does not work properly. Strange thing is when I view my feed through some tools ( http://www.threadless.com/profile/685752/tyshcr ) - it is properly updated.