I can understand the limitations on bandwidth, AJAX search filters etc would put a hell of a lot of strain on the db.
I wouldn't have thought RSS would make much difference, disk space and read write times may impact but from a bandwidth point of view I would have thought it'd be a little better. For example, to get to thie post, I would visit the index page, then maybe go to the software sub section, then HTML, Graphics & Programming, then this post. So through introducing an rss feed i'd save on the bandwidth used to display what 3 or 4 pages, the images that go with those pages etc....?
Or am I missing something?