> If you're employed "at will" (and almost everyone in the US is) you can't refuse "promotions." From the company's perspective they are deciding to no longer employ you for position a, but they are simultaneously offering to employ you for position b. You can take it or leave it.

That's not correct. Being employed at will means that you _can_ be let go for refusing a promotion (or just about any other reason) but it doesn't mean that automatically happens. There are plenty of companies that understand that some people reach a point where they don't care about climbing the ladder anymore and don't want to take on more responsibility.