The numbers are suspect.
But whatever the true numbers are, it is worldwide. Mostly in poor countries where the majority of converts fall away within 2 years.
If the LDS church has such a high rate of inactivity, they wouldn’t be creating over 350 Wards or congregations every year. That’s nearly 1 a day. Why spend so much money on an empty building?
Here is an interesting look at the growth of the Church worldwide up to the year 2004.
http://www.youtube.com/watch?v=h_7qTaGejuY