Not sure this is the case in all configurations, YMMV. In SharePoint 2010, it seems like blog commenting isn’t “on” by default. Everything should work fine but once you start posting, other people won’t be able to add comments even though there is a comment link at the bottom of each post. How to get it blog post comments working? A few basic things that I will go into detail on.
First, get to your blog “site” in your browser, and go to “Site Actions->View all Site Content”.
Once there, you will see that Categories, Comments, Links and Posts are just SharePoint lists. Pretty cool. Go into the “Comments” list.
Once in the Comments list, click on “List” at the top, and on the List Ribbon click “List Settings”.
Click on the “Versioning Settings” link. In there, you want to check the setting:
1. Require Content Approval for submitted items? – yes. if you want to have some gatekeeper between new comments and them being published.
Under “Advanced Settings” link
1. Item-Level permissions. You want “read all items” for Read Access and “Create items and edit items that were created by the user” for Create and Edit access.
In the "Permissions for this List” link, you want to probably break Inherited permissions, and then add “Authenticated Users” with “Contribute” and “Read” permissions.
As a final setting, you want to probably get alerted on new comments. So back on the main “List” ribbon, you want to click on “Alert Me” and set up the appropriate alerts, or subscribe to the RSS feed.
That does it, after going through all those motions, you should be able to have other people comment on your SharePoint 2010 blog, get alerted, and approve comments. Pretty cool (For what it’s worth, this shouldn’t be this complicated!)
Steve Novoselac's Blog 