The comparisons you make are on absolute terms but the reality is more nuanced. There are almost 47 million people living in poverty in the US [1] and something like 38% of the population live paycheque-to-paycheque (up from 31% in the late 90s) [2]. Even if most of those people are food-secure (something like 90% of Americans in poverty are) those numbers should still be pretty alarming. Just because the average American has it much better than the average African doesn't mean their situation is necessarily very good.
[1] http://www.census.gov/hhes/www/poverty/about/overview/index....
[2] http://www.cbsnews.com/news/more-americans-live-paycheck-to-...