The point 1) is only partially true. For example, I don't have any friends on Twitter, but I use tweetscan to search twitter, when I want to see most current events about something...for example, I want to buy some newly announced gadget, so I do a search now and then to see links to new reviews, or short ideas from early users about how they like or dislike it.

I think this might by one reason why twitter is so popular - it can be used for many different purposes.