I just began to aggressively persue SEO for my sites. On the main page on one of my sites the Google ranking stayed a 1. However, on other pages it's a 2 to 3. The major content is on the main page. The only thing I can think of is that I changed the index page from a .htm to .php a few weeks ago. SEO does work. In just a few weeks, my 3 sites jumped for 1 to 3 on several pages. What is wired I have a link directory on one of my site and it jumped to 3. There is hardly any content on it. Go figure.
Its all depend how you made your site visible to Google. Main page or sub pages does not matter for Google.