1) Close, yes. Your blog always hands out the most recent “x” number of posts, based on the configuration at Options -> Reading. It’s up to the feed reader to figure out what it already knew about and what it didn’t — and, optionally, alert the the user to edits/changes in existing posts.
2) See 1. I’ve not really paid attention enough to notice if IE7 -or- FF handle flagging edited posts in feeds.
3) To the best of my knowledge, WP does not include Pages in feeds (reasons given earlier in this thread).
4) They get all the feeds you provide. Some just don’t notice the edits.
5) First issue: This is a new wrinkle that we hadn’t touched on yet. There are multiple ways for your feeds to be “discovered”. The obvious one is your feed buttons on the sidebar. However, modern browsers and feed readers may also look for hints in the <head>
tags of your blog.
For instance, in my theme’s header.php, I’ve added the following code:
<link rel="alternate" type="application/rss+xml" title="RSS 2.0" href="<?php bloginfo('rss2_url'); ?>" />
<link rel="alternate" type="text/xml" title="RSS .92" href="<?php bloginfo('rss_url'); ?>" />
<link rel="alternate" type="application/atom+xml" title="Atom 0.3" href="<?php bloginfo('atom_url'); ?>" />
When the page is rendered, that looks like:
<link rel="alternate" type="application/rss+xml" title="RSS 2.0" href="<?php bloginfo('rss2_url'); ?>" />
<link rel="alternate" type="text/xml" title="RSS .92" href="<?php bloginfo('rss_url'); ?>" />
<link rel="alternate" type="application/atom+xml" title="Atom 0.3" href="<?php bloginfo('atom_url'); ?>" />
and tells the feed reader that I’m offering three RSS formats. This is what drives that selection you see when clicking the feed icon in the URL bar of your browser.
The category feeds are something that you’d likely offer as links in your side bar (in fact, wp_list_cats can do that automagically). Works nice if your blog covers a variety of topics and some of your readers only care about one of them.
Hope this all helps in some way!