Based on a report in the August 23, 2012, PDF copy of The Wanderer, Fr. Zuhlsdorf offers a detailed analysis HERE concerning something he describes as "pretty important."
Fr. Z's concluding summary:
By this response, the PCED is clarifying that those who want the older form of Mass do NOT have to admit that practices such as Communion in the hand, or altar girls, or EMHCs, etc., are good. They might be legal, but they might also be abominations in the sight of God ... depending on your point of view. Furthermore, a priest or a bishop cannot say “Because your group, over there at St. Cunigunda’s in Frostbite Falls, denies the ‘legitimacy’ of altar girls, you therefore do not quality as a stable group that can ask for the Extraordinary Form.”