I agree with you. I'm saying that unless you're negotiating for the job of "EVP Sales North America" or "Chief Operating Officer", no contract at any level of employment from intern through janitor to engineering manager is going to insulate you from the employer's right to change their mind. As I'm sure you know, the right for employers to change their mind is one of the fundamental features of the US labor market.

It's generally a good thing, too.