I suggest you to read this - Readers can't comment on your blog - Tip For You
With a very little change to your template you can add this hack to your blog.
This hack was originally posted on thisischen
Update - Previous Reply code was not working for some blogger templates.This is an updated version and work well with all templates
Adding Comment Replies to your blog.
Step  In your dashboard Click 'Layout' > 'Edit Html'> Tick the 'Expand Widget templates' box.
Step. Paste the following code Directly Below/After <data:commentPostedByMsg/>
In order to make this work you must add your blog Id .
What is your blog ID??
Simply go to your layout page, posting page or any of the pages and copy your I.D. from the address bar at the top of the page.
Replace URL of image with any image of your choice or you can choose one from below-
Add This Reply to comments blogger hack to your blog and Do tell me if you like this Concept.