they act as though only the rich can buy an envelope to drop keys into... Actually, I think the point she is making is that the wealthy are the one mose often doing this, and that she thinks the middle class should be doing it more.
She's not treating it like a negotiated agreement. She's leaving the impression that the rich are walking away and getting away with something. If members of the middle class acted without full understanding - and 'mailed' in the keys, their credit would be ruined and they would still be responsible for loans against their house. As would the rich or anyone else for that matter.
You have to remember who she writes for - and that her 'groupthink bunch' hates the middle class. Her advice is designed to inflict class envy - it's not designed to help anyone...