Generally comments are not displayed on the main page to make navigation easier, especially if you get lots of comments, or long comments. I know a number of people that get 300 to as much as 700 comments on each post, and raincoaster has one with over 2000 comments. Can you imagine having to page up or down through all those comments just to get to another post? Some sort of collapsable ajaxified comment thing would work, but that isn't possible here.
Check out the P2 theme. That is the only one here that will show comments on the main page, and has a toggle to show or hide comments on each post. Do be aware though, it is a bizarre theme in some ways and is designed for collaborative types of things. It is sort of like twitter without the 140 character limit.