Raincoaster will actually be the one that is likely to know all the ins and outs of this since she knows a lot about this stuff, but I would guess that part of the reason that some of your posts and pages outrank the main page is that they are constant and are getting a lot of clicks from search engine results. I have a couple posts on my blog that consistently get way more search engine referrals than most all the others combined.
The blog main page is constantly changing with new posts being added all the time, so things move off of it regularly as you add new posts. Most people searching on the internet are entering phrases and such for things they want to find and typically when they find it, it is going to be a post. Main pages on blogs just change too quickly to build up a lot of page rank.
That is sort of my theory. Raincoaster will correct me if I'm wrong.