I don't think that this metric is bad for the US citizens.
We need to know where those money go to. Do they shop or do they invest them? If the latter happens, then this is a crucial factor which provides growth to their income.
US tax and mortgages consume large percentage of the income though they seem to have one of the highest income in the world. US citizen also have a bad spending habit. They get into debt early and pay all the their lives. Their risk taking ability into making more money is lower in US citizens than for foreigners.