If I assume that there is a link from the index to the blog post then we've seen this behavior before: the page with the link on it being returned in the normal SERPs rather than the expected one. Suppositions abound. It's possible, maybe, that it has something to do with this patent filing [appft1.uspto.gov], though the behavior was noticed some time before the October 2007 filing date.
Web pages of a Website may be processed to improve search results. For example, information likely to pertain to more than just the Web page it is directly associated with may be identified. One or more other, related, Web pages that such information is likely to pertain to is also identified. The identified information is associated with the identified other Web page(s) and this association is saved in a way to affect a search result score of the Web page(s).
Mostly just food for thought as G always has something new going on behind the scenes. It's just hard for us to suss out what it actually is.