To get a grip on "why" the @twittername mention is important in a RT, go sign up (free) for klout.com --
Or just look at my name there http://klout.com/JLichtenberg (I made 57 once)
Klout.com is a "service" that rates "reach" (i.e. how important you are on the internet) via twitter responses and it accesses some other social network activity metrics too.
The number klout.com comes up with is used by search engines to suggest you as the answer to various questions, (or at least it was last I looked). There's a whole lot of reasons why your klout number is the key to selling books.
There are probably other such services out there -- but your Klout number comes up on hootsuite.com window when you click on the @person name on a tweet.
It's all about "who" you are to "the world" -- as writers, we gather followings. I think most of us have READERS following us, and "readers" as a group tend to be more "influential" in the world -- so if we team up and RT each other, expanding the "klout" "reach" we each have, we can become the answer to search engine questions, and sell books.
Roundabout, but it's not much effort to put an @person in a tweet if you use hootsuite -- it auto-completes the @ if you remember the first couple letters.
Twitter itself is not much use for anything. To "work it" you need "tools" -- Tweetdeck and Hootsuite seem to be emerging as top favorites of those serious about mastering social networking. (try free versions)
Jacqueline Lichtenberg (freebie enthusiast)