This pope is wrong in this statement.
While I believe that there is no Christianity other than Church Christianity, I do not believe that the Roman Church is the sole place one finds Christianity on this earth.
For what it's worth, xzins, I don't think Pope Benedict thinks that either. Please take the time to read this amazingly powerful Encyclical: It is addressed to Christians, not just to Catholics. And then, if you have the time, read Aiden Nichols' The Thought of Benedict XVI, and draw your own conclusions.
This Pope is extraordinarily ecumenical in his thinking. He does not believe that the Reformed Church in any of its departments is "outside" Christianity or salvation in Christ. He takes the thought of Calvin and Luther very, very seriously, and admires these men as great spiritual thinkers.
Go look for yourself, if you have the time and interest, and see if you disagree with my assessment!