Unfortunately I fail to replicate the assertions of the article, using the World Bank's povcal tool. [0] ( Linked in the article.) As far as my clicking around goes, it seems that a strong reduction in poverty is independent of the precise poverty line used. In particular, if I use a poverty line of $2.5/day (2005 PPP), the data shows a reduction from 75% of global population to 46%, contrary to the claim of the article.
So just a bit playing with the data seems to imply that the claim of a strong reduction in global extreme poverty seems to be warranted. (This is certainly not a sciency study...)