URLs have www. instead of http://

Actually, it's a bug in TweetDeck. Twitter itself accepts URLs with 'www.' instead of 'http://' just fine, as do most other services that comply to the Twitter API standard. Tweet uses www. instead of http:// because it makes the tweet 3 characters shorter.

If you insist, you can change this behavior by editing tweet.module. You need to remove this code:

  //Replace "http://" with "www." if the URL is abbreviated because it's shorter.
  if ($url != $q) {
    $url = drupal_substr($url, 7);
    $url = 'www.'. $url;
  }