Processing Meeting Responses
I send many calendar invites. The "accepted" response shows up in my email but the "status" remains as "no response" and I have to go in and manually change the status.
Most likely the problem is that you don't have Outlook configured to automatically process meeting responses. In Outlook 2010 - Go to File | Options | Mail and scroll down to the Tracking group.
Make sure that the box for "Automatically procss meeting requests and responses..." is checked. If it's not then Outlook won't try to do anything with those responses.
By the way...this is also the way to stop Outlook from adding a "tentative" appointment to your calendar when you receive a meeting request from somebody else.