Interestingly, this article doesn't even touch upon the real challenge: It's not in mass producing these items at low cost; it's in gaining widespread distribution to those one billion customers -- across different countries and cultures, to thousands of groups of people each motivated by different things.
Motivation is key. It's hard to figure out what motivates people, and it differs enormously across cultures. You could have the most effective $100 house around, and you could even have a way of distributing the physical product to hundreds of thousands of people living in poverty. But what happens when no one wants to live in your house -- because, as it turns out, your house is foreign, not cozy; it just doesn't feel like home.
Does that seem like a silly example? It's not. The poor are not as easy to figure out as some people think. Understanding their motivations -- immersing yourself in their cultures and understanding what they really want, what really drives them to make certain decisions -- is the key to good design.
And, unfortunately, it's an aspect of good design that's not easily scalable.
Obviously, there are pockets where you can start and grow from. But saying that a billion people are waiting for $100 houses -- as if the only issue is designing that damn thing to get the price down! -- strikes me as not being the best way to begin a dialogue on poverty alleviation.