Twitter's security model is utterly bizarre. If you are blocked by someone on Twitter you can still view all their updates via the web on their root Twitter page. The only thing you don't seem to be able to do is read an update on its own unique page when you are logged in. If you are not logged in you can read it (unless they hide all updates all of the time to everyone but friends).
The only functional thing I can see in blocking is that you don't see "replies" that mention you from those you have "blocked", but it doesn't stop those you have "blocked" talking about you publicly or reading you. So, pray tell, what's the point?