Click the post title or comments link please and scroll to the end of the post.
The way your theme and blog are functioning is the norm. Unless you use the P2 theme which is a Twitter-like theme, know that the front pages of our blogs "showcase content" and comments are collapsed on that page. You cannot change this. The way the comments function is coded into the core of WordPress. By clicking the post title or the comments link the posts on the front page open on their own page where all comments display.
Some themes display comments bubbles (links) at the top by the post title. Most do not. What I posted applies to every WordPress.com blog regardless of theme.
I have nearly 1000 posts in my blog. Imagine how long the page loading time wold be if every comment made over the last 7 years displayed. I wouldn't have any readers because they would be so peeved off at the lengthy page loading time they would click out before the blog loaded.
Also note that to display excerpts of posts only on the front page of the blog followed by read more links visitors can use to click to read the full post on its own page you can insert the more tag into your posts. http://en.support.wordpress.com/splitting-content/more-tag/ That will reduce page loading time. Don't forget that many are still on dial-up service and they pay for every minute it takes to load the blog.