That being said however, I do see this behavior creeping even into settings where I didn't notice it 2-3 decades ago. This tactic only works as long as there is some sink to offload the negative externalities to; that is, everyone else who does not negotiate this way. Developers who are made aware of this "negotiation" style on the other side should make every requirement request an adversarial minimax engagement where they seek to do the least amount of coding for the most profit.
Even today, if you pull similar stunts during negotiations where you perform Clintonian-grade-gyrations through the attorneys, or even more minor shady acts, in my small part of the industry people remember that for a long, LONG time. Word gets around. It follows you from employer to employer now, with the better sales tracking we have these days. And where other customers get cut a lot of slack just for being nice, you're going to be fighting for every micrometer of delivered support. Just because once you set a precedent, no one will to want to get caught on the other side of one of your "gotchas". Good on ya if you have the energy for doing that all the time, but I'd rather be using the time more productively myself.
Coase's theory of the firm and its subsequent expansions by other researchers would find that when everyone engages in this style of negotiation, transactional costs skyrocket. I've had one customer who was particularly enthusiastic about this style of dealing with vendors. We dumped that account onto a competitor.
We're talking about something different here - a potential hire joining a company and asking for "X% of the company". If the company agrees to this, then the legal document better not say you got X% of the employee option pool. That kind of shit is obviously going to ruin your employee's trust, because it's extremely fucking shady. I would immediately get the impression that the company/founders are big scammers.