If I needed $80k, I would then say "I'm sorry, but I have expenses to pay, a family to keep. I can't work for less than $80k." If he insisted, that's when I would shake hands and walk. It wouldn't matter, in fact, if he was being honest or not. That's my limit. In this case, it's no different to bidding on eBay: I have $80 for this purchase, if it goes higher I will maintain self-discipline and drop out of the auction.
It's less so in the IT world right now, but in most other fields, there's much higher unemployment. People don't "just walk away", and often accept a situation that doesn't fit their wants/needs, because needing income ends up trumping everything else.
For someone not in IT right now, who needed a job, they're at a strong disadvantage because of the information imbalance during interviews. Congrats on you being a rather rare individual who actually does what is recommended (walk away) - most people don't. And it comes back to not being able to tell if the other side is lying. And in some cases, being desperate enough to work for/with someone who they suspect or know is lying, but needing the job bad enough.
The big point in the earlier discussion this week was that you don't know if the other party is being honest. They can do background checks on you, credit checks, employment history checks, etc (with your consent of course), but you have no idea about their background. With public companies you can read some info about them, but it's not personal, nor does it go in to departmental politics and budgets and such.
A potential employer saying "our hands are tied, we can only go up to $75k for this position" may be telling the truth, or they may be lying. You can't tell the difference. That was the gist of the earlier posts.
"Be prepared to walk away" is core negotiating advice for any commitment - marriage, car purchase, job search, housing, etc. Not having the guts to walk away means you will make decisions based out of fear, rather than out of a position of strength.