My 401k is the perfect example of how nothing takes the place of marriage.
It was a simple matter, once upon a time, to put my wife's name on the primary beneficiary line and my kids on the contingent beneficiary lines. Now I am forced to make some unsatisfactory choices. I can put my partner as my primary beneficiary or I can put my children. There is no choice for contengent beneficiaries. Or I could designate my estate as the beneficiary and my survivors can fight it out in court. Or I can designate the trustee of my will as beneficiary, in which case they may still end up fighting it out in court. There is no simple, reliable way to say I want my partner as primary and my children as contingent beneficiaries.
Just like marriage... mm hmm.