Agreed. Plus, not understanding the RT abbreviation probably means that all the "@username" retweeting "@originalusername" is pretty confusing, too. At that point, you either get Twitter syntax or else you don't, yet.
Since tweets are all about brevity, shorthand seems like a smart move. Some abbreviations are difficult to understand, but in the evolving lexicon of the twitterverse, this is seems like a no-brainer to improve and enhance the taxonomy of terms underpinning the lingo. IMHO