I think the real point isn't that you get real-time updates, but that you aren't constantly polling the server only to find that there are no new updates.

RSSCloud (or something similar, ideally based on XMPP, I'd think) will be a huge bandwidth saver once most of the sites on the web are using it, because they will *never* have to ask the server if it has updates, because the server will tell them instead.

It's not so much about saving time or bandwidth for a given reader, since it doesn't take much to poll a site every so often, but the bandwidth savings for a popular site could be much larger.