A billionaire does not have a room of dollar bills either.
You can withdraw your contributions to ROTH IRA's at any time, penalty free and ROTH 401(k)s are easily rollover-able to a ROTH IRA.
They are completely a part of net worth, it's in the very definition.
Retirement accounts hold YOUR money, that is money that YOU saved for YOUr own use later.
Whether I put it in a savings account or taxable investing account it is still part of my net worth as it's money I will be using some time in the future.
Perhaps I'm too dense but I'm not understanding why you are not including retirement accounts as part of net worth calculations.
If you don't see any value in that, then I'm sorry, the next time I won't mention it. My apologies. I repent.