Here's the crucial way Twitter differs from other forms of communication (post, email, phone, face to face). With the other forms, you first find the person you want to communicate with, then direct the words at them.
With Twitter, the people are almost impossible to find first. They use aliases, they compress their real names, even the best directories are hit and miss. Besides, they're probably not paying attention. As for lists, they don't list people – they simply list fragments of conversations.
So, with Twitter, you can't find the people first. You have instead to find the conversations either through targeted searches or through a laborious process of following and listening. Once you find the conversation, you're likely to find people interested in it.
If you think this sounds familiar, it echoes the 'situational theory of publics' articulated by James Grunig a quarter of a century ago. Publics form around issues; people gather around conversations. It may not be intuitive, but it makes sense.