I'd probably wager they (the NFL) would like to expand the interest in the sport. They've done preseason games abroad plenty of times (including this year), however those games aren't real (players are held back, this years Peyton Manning vs. Micheal Vick wasn't anywhere near as good as it would have been if it were for real). This is regular season and you can tell the fans like the scoring (they boo when they punt on 4th or go for a field goal or kneel the ball down with 6 seconds to go in the half). Who knows, with teams in Europe, maybe the NFL is looking to start some sort of system in the central/southern Americas.
I think LA got the go ahead for a new team, not sure when, but just one team would unbalance things...