I think there are different tables if people are still using the old style W4s.

The new style W4s are designed to make you break even (within a few hundred bucks either direction), so your guy with 50k in earnings, 50k minus the standard deduction leaves him about 37k in income, that gives him a tax liability of approx 4200, so thats pretty close to his 4000 in withholdings, which means he didnt give the government free use of his money all year, he got it all in his paychecks..