It looks like Twitter is now in the process of deciding how they can please everyone all the time. Its most recent change to its service is to eliminate the option to see @replies that involve folks you don’t follow. Here is part of Twitter’s explanation from their blog
We’ve updated the Notices section of Settings to better reflect how folks are using Twitter regarding replies. Based on usage patterns and feedback, we’ve learned most people want to see when someone they follow replies to another person they follow—it’s a good way to stay in the loop. However, receiving one-sided fragments via replies sent to folks you don’t follow in your timeline is undesirable. Today’s update removes this undesirable and confusing option.