Has anyone tried to add special clauses to their initial contract along the lines of: "If the offer is rescinded before the start date, the applicant will be awarded 3 months salary. If the applicant is fired within 3 months of the start date, the applicant will be awarded relocation fees to previous location." And you'd update that based on costs of moving, or possibly the state of the economy and your risk toleranc…
Unless you are a special snowflake with a unique skillset, why would a company the size of Amazon ever veer from their standard contract?
No one can operate a company as a single giant monolith. They're all subdivided into departments or subcompanies or subunits in some way or other. And these subunits often have more or less leeway and authority to act by themselves (depending on the exact organization).
My favorite story is when the manager across from me happened to have signing authority for the relevant subunit. So he just grabbed a sheet of A4 out of the printer, scribbled down what we agreed upon, put his signature under it, and handed it to his secretary "Please file this in Kim's file". Didn't even blink. Another time I made a cultural mistake, I actually gave a Very Large customer my best offer upfront (negotiating as a small company owner this time). I should have tacked on 20% or so, just to give the manager something to negotiate over. Lesson learned: Big company managers aren't just able to negotiate; some actually almost feel cheated if you don't give them anything to negotiate over! ;-)