Why do we retweet our friend's tweets? Do we really retweet them because they are valuable, and we want to share them with others? Ok, this is one possibility, but in fact, the real motive behind retweeting a post is that we find it valuable, so we attach our names to it, and wait for others to retweet our retweet with our names attached to it. It's the ego-factor that drives us her, and not just the love of sharing good stuff with others.
Such scenario worked really fine with the old manual retweeting system, but now with the new retweeting button, our names are removed from the heart of the tweets, and are replaced with a tiny picture at the bottom of the tweet, that no one cares to look at or click on it.
And that's why I believe that the old retweets will continue to be used, and the new retweets will only be used by lazy people like me, who are too lazy to press ctrl+v and ctrl+c.