...in the U.S., growth is mainly in hispanic congregations, not in english speaking areas? And yet, everybody here has pretty much the same access to the internet...
There may be some cultural differences at work here too. There are many economic and social groups within the U.S. I wonder what the internet penetration is among Hispanics.
Also, in my limited experience, Hispanics as a group are very submissive to, and respectful of, authority. For those who are already JWs, if the Society says 'stay off the internet,' they are likely to comply, the result being fewer defectors from the Watchtower. If the number of defectors eventually increases, the number of new ones coming will likely decline as well.
This is the cause and effect the Society is fighting so hard against. (The cause: people becoming informed via the internet, and many leaving the Org. The effect: Less people to declare their message, less zeal among those left in, resulting in lower increases.)