@Reminscence, I agree that our economy relies heavily on the working poor to keep the wheels moving, but I think the article was focusing more on poverty, not underemployment. There are people who have lost all incentive to improve their lot in life, and there are several theories about why that is. Personally, I think poverty happens because most countries, the US included, oversell the idea of success. Yes, a child can do everything possible to become a paleontologist or a circus performer, if that's his or her dream. However, the reality is that the world only needs a certain number of people who search for fossils.
Even on a smaller level, not everyone is going to find gainful employment unless a country's economy is running white hot. Some people are just not going to have an opportunity to get higher paying jobs, regardless of native ability or education level. Poverty is a sad side effect of capitalism.