> Personal income as defined by BEA differs substantially from adjusted gross income (AGI), the principal income measure used by the Internal Revenue Service.

So it explicitly is not the same as the IRS definition of income.

> For the measurement of personal income, employer contributions to pension plans are counted as part of supplements to wages and salaries. Employee contributions to the plans, capital gains of the plans, and payments of benefits by the plans are not counted as part of personal income.

I believe they consider a 401k to be a defined contribution pension plan. I know normally you wouldn't call a 401k a pension and you wouldn't talk about "payments of benefits" from a 401k, but in context (page 32) I think that is what they mean. So it seems like the amount your employer contributes to your 401k counts as income for that year, any additional voluntary amount you contribute doesn't count, and when you withdraw money that also doesn't count. Maybe I'm misunderstanding but that is my reading.