CIG has said that they have been working on a new patch client that will work quite differently to allow download of only modified files.
CIG promised a new patcher quite some time ago, nothing came of it so far. Their past and current behaviour makes their promises matter very, very little. Besides, I don't see any inaccuracies in Backer 42's statement, current patcher does download few very large files. The claim of bandwidth charges being a motivation for changes in the testing process was corroborated by a statement from someone in CIG, but I would have to dig quite deep to find it right now.