Apple is a company that doesn't often jump bandwagons; they rather have everyone else jump on theirs. It is thus somewhat understandable that they don't have an official Twitter account yet, except for the one that lists all the new iTunes Trailers.
However, as noticed by Tweetdeck founder Iain Dodsworth, Apple has recently added a couple of iTunes-related Twitter feeds, bringing the total number of their accounts to five. These are:
It's not much, and we'd still like to see Steve Jobs tweet, but it's a start.