I don't disagree with what you say about the relative advantages and disadvantages of Twitter vs. RSS as a means by which individuals discover content, but there are important technical aspects of RSS that are independent of people reading aggregated feeds. That is to say, if no-one ever used a feed reader or iGoogle or any other subscription mechanism, there's important roles for RSS.

Among these are the structured aggregation of feed content by search engines. To take just one important example, basically the only requirement to be listed in Google Blog search is that a site have an accessible RSS feed. A post is published and it appears there, making that content available to searchers, regardless of whether an actual human aside from the author has vetted the post.

RSS can also be used to populate sites (either as individual or topically aggregated feeds), often with a high degree of granularity (e.g., tag feeds). Depending on how robust these feeds are, the level of detail can also be specified on an included feed – linked title, title and description, pictures displayed or not, etc.

My basic point is that it's limiting to think of RSS solely as a tool for users (that is, for example, in thinking of the value of RSS for the site as being the number of subscribers for a feed), because it's a more broadly-based technology tool.

Oh, by the way, found this post through my RSS feeds.