I don't think that data supports the claim that Twitter is a one-way medium. What it shows is that there are a significant number of Twitter relationships which are one-way, but that doesn't mean that any individual is solely using Twitter as a receiving medium. What you would need is data on the number of users with no followers who are still reading their timeline; in the linked post, Dalton says this is high, but doesn't provide a link and I can't find data on this.
"I'm not convinced that this is true. Here look at this random kid I picked. Nearly everyone he's following looks like a peer:"
This is the problem with inferring statistical properties from a sample size of 0 or 1. Here's some data on the subject: http://www.intmath.com/blog/twitter-follower-semi-log-graphs...
The sharp drop from having 0 to ~1000 followers on the graph on number of followers indicates that twitter is somewhat of a one-way medium.