Since poor folks have _always_ been underrepresented in the official stats, John's suspicion has to be grounded in evidence that poor folks have been _more often_ under-counted than in the past, I think.
That said, since one feature of neoliberalism is a growth of what is called "informal economy," John's suspicion that official stats are increasingly unreliable (compared to, say, the period from the Korean War and the Oil Shock) may be valid after all (more valid in poor nations than rich ones, since poor nations have much bigger informal sectors than rich ones do -- hence the difficulty of taxation, corruption, etc. in poor nations).
As for the impact of incarceration rates on unemployment rates which I believe John mentioned earlier, the growth of the prison-industrial complex must have an effect of decreasing unemployment rates & thus raising the median wages of lower-income-bracket workers (by taking adult males of prime working age out of the regular workforce & creating many jobs, both in public & private sectors), no? At the same time, the wars on crimes & drugs have made costs of living higher (& lowered standards of living) for an increasing number of people, since fines, court costs, lawyer fees, bail bonds, etc. must be paid & prisoners can't contribute to household incomes (through regular or unofficial jobs) & instead have to be supported by their families. In short, fighting against the criminal justice system has become a part of daily necessities for the poor, but this fact is ignored when economists discuss "standard budgets" & "official poverty lines," I believe.
Yoshie