That's very true. Maybe a better Twitter could incorporate actual geographical distance. You would have to choose where you are and could only see messages from people that are actually near you. If you move, you see different messages.
Or the distance could be ideological -- or better, theoretical.
Any user would have to choose a place on a "map" / a set of coordinates. A user can move freely at any time, but
- messages can't move and stay where the user was when they were posted
- messages can only be seen when the user is near them.