I've been planning to write a column or speak on the radio about this for a long time and I'm happy that Amanda Carpenter beat me to it. Her observation on fashion and make up being to women what sports are to men, is one of not insignificant sociological depth. What we talk about and consequently what we're interested in is a function of the group we talk about it with. And the discourse (and even the interest) has a dimension of group utility.
What is the difference between a discourse analyst with training in linguistic methodology and a blogger or the reader of a blog? Discourse analysis relies on the human capacity to understand text but it is also embedded in the social practices of discussing and inferring the meaning from text. The following example of a simple computer-generated graphical representation of Obama's speech (courtesy of Wordle.net) in many ways does the job of half an academic paper. It presents the data and lets the reader infer meanings (particularly in comparison with other speeches).
Obama and swaying fields of corn was a major theme of his 30-minute pre-election and then Elizabeth Alexander's poem at the inauguration brought it home during the inauguration: