First, there is just the global distribution argument.
Then there's the dynamism/adaptation argument: a recent NYT story talk about how parts of the Brazilian church are "countering evangelicalism and secularism with livelier worship."
Why?
Market shift:
So both the center of global gravity in the church and its most likely form of marketing salvation.
Brazil is experiencing a huge expansion of its middle class. People undergoing such tremendous socio-economic churn want moral handholds. But they also want it in a form that they find conducive to their daily lives, and the traditional Catholic church has simply changed too slowly in response to the competition.
I saw a version of this in Ethiopia two years ago. Place is booming and all sorts of change happening. The classic Ethiopian Christian faith - very Catholic in form - just wasn't getting it done. But you'd see these evangelical churches (mostly Pentacostal) everywhere and they'd be packed (I mean, with crowds extending out into the street!) - and jumping.
My fear with Benedict is that he retires so he can - in his typical control-freak fashion - determine his successor. Let's hope it's something more than personal ego at work here.