There is another way to characterize the trends that Paul Graham observes. Perhaps growing economic inequality is a natural consequence of capitalism itself, and the "defragmentation" (or greater economic socialization) of the economy brought about by World War II was only a temporary reprieve from the overall trend toward greater inequality.
This view is essentially Marx's original critique that, given enough time, capitalism will destroy itself. As wealth accumulates at the upper end of the income spectrum, it has a self-reinforcing and accelerating feedback effect: greater wealth purchases greater political and social influence, which enables even greater wealth production, often at the expense of the poor and the less wealthy. The system inevitably sows the seeds of its own destruction.
History has shown that massive inequalities lead to instability and revolution. As a self-admitted beneficiary and generator of said inequality, Graham is right to be worried about how he would do during such a period of instability.