Because this case involves First Amendment issues, terms that were in use by citizens when the Bill of Rights was drafted may help in understanding the legal context of Blogs and Twitter. Suppose that a Colonist erects a bulletin board in the front yard of his home to post announcements that might be of interest to others and other Colonists do the same. A Blog is like a bulletin board, except that it is erected in cyberspace rather than in one's front yard. If one Colonist wants to see what is on another's bulletin board, he would need to walk over to his neighbor's yard and look at what is posted, or hire someone else to do so. Now, one can inspect a neighbor's Blog by simply turning on a computer.
I'm an Israeli lawyer, so I'm amused that "terms that were in use by citizens when the Bill of Rights was drafted" help to explain anything.Twitter allows the bulletin board system to function so that what is posted on Colonist No. 1's bulletin board is automatically posted on Colonist No. 2's bulletin board for Colonist No. 2 to see. The automatic postings from one Colonist to another can be turned on or off by the owners of the bulletin boards, but there is no mandatory aspect of postings on one Colonist's bulletin board showing up on the other's. It is entirely up to the two Colonists whether their bulletin boards will be interconnected in such a manner.