This sharp reduction is pretty much entirely down to China.
http://news.bbc.co.uk/1/hi/business/7583719.stm
This article makes very misleading claims, confusing absolute poverty with extreme poverty. The last sentence is horrendously inaccurate, about 985 million are below the $ a day mark (which doesn't allow for inflation since 1981, making it an unfair comparison)... they must have missed the 1 in front of the 5.
Still, it's good that so much progress has been made.