During the downturn, America's poor helped each other more. The rich pitched in less.

The big story here, to me, is the increasing power of fewer and fewer people. That's to be feared.

More to the point of the article, though, I believe this can be largely explained by affinity effects. You trust people like you. The upper class closes rank, leaving the lower and middle classes to help each other out:

Since 2009, a rising economic tide has mainly lifted yachts. During the recovery, the gap between the rich and the poor has widened. Both in terms of incomes and wealth, the rich got richer. Meanwhile, the poor and middle class either saw their earnings and wealth stagnate or fall off.
And yet amidst all that, something odd happened. Even during the downturn and recovery, the poorest Americans upped their charitable giving. Meanwhile, the highest-income people gave less and less, the Chronicle of Philanthropy reported this week.