Clarifying how the Church established by Christ subsists in the Catholic Church

The Holy See clarifies why it uses the word "subsists" rather than "is" when Lumen Genium declared:

"This Church constituted and organized in the world as a society, subsists in the Catholic Church, which is governed by the successor of Peter and by the Bishops in communion with him,(13*) although many elements of sanctification and of truth are found outside of its visible structure. These elements, as gifts belonging to the Church of Christ, are forces impelling toward catholic unity."

Why is this being clarified today? Papa Benedict has been steadily and firmly working towards visible Christian unity. The recent motu proprio which clarifies the perpetual validity of the Tridentine Rite also points out the unacceptability of broad and liberal experimentation with the liturgy. This reaches out to those who reject the Novus Ordo because of grave liturgical abuses of the past generation or so. This clarification on Lumen Gentium is also relevant to the same people, some of whom protested at the word "subsists", so strong was/is their need to reject false ecumenism that was grounded on politeness and relativism. This also reaches out to the Orthodox Churches, our sisters in the East. But how do Protestants react in the way they are addressed? I guess we'll have to wait and see if they react at all. In any case, I think the clarification is about being precise, which is a necessary ingredient in true dialogue anyway.

Updates: A very good follow-up at the blog of Fr. Philip N. Powell. The Pertinacious Papist identifies a very good Evangelical response. And Lito at extra nos says "I told you so".