I am enjoying this conversation, and just have a couple of points to add to it.

First of all not only does Odlyzko not discuss public vs private, he also doesn't really discuss commercial vs non-commercial. For instance in the point to point category he includes phones. But telephone companies generate substantial fractions (the majority?) of their revenue from calls involving companies, most of whose traffic is likely to be commercial in nature. What he really discusses is whether broadcast commercial content can pay for a peer to peer network. (No.)

Furthermore the public vs private distinction and the broadcast vs peer to peer one both seem to me to have a hazy boundary that is fuzzy and fading fast. At one point to engage in public broadcasting of information was fairly difficult. It needed substantial facilities for production and distribution. This barrier to entry created businesses whose natural job was to be a bottle-neck between would-be content creators and potential content consumers. Both natural bottlenecks are fading because of improvements in technology, but organizations of those companies are attempting to create new barriers to protect their businesses. (Think RIAA and MPAA.)

However there is a growing group of semi-public, semi-broadcast models. Part of it is in online forums like this one. Publically mirrored email lists. Blogging. Online comic strips. And so on and so forth.

These are publically accessible. But the vast majority of the content produced is consumed by small groups of people who mostly know each other. This is public in the same way that my conversation with friends on a street is public - someone walking behind us can listen in. In reality it is basically peer (me) to peer (small circle of friends). However straightforward power laws indicate that you will see an entire spectrum from personal discussion up to circulation numbers that professional columnists can respect. With no division between them.

Of course this is communication without commercial aspirations behind it. From Odlyzko's point of view, it makes broadcast payments even less able to pay for content. (A trend which doesn't make companies based on generating profits from broadcast bottlenecks very happy...) But I find it an interesting blurring of boundaries as what had been a private activity (talking among friends) shades into clearly public consequences.