I've seen employers tell my ex- that they were looking for someone to commit to multiple years, not just be fly-by-night. She agreed, and was laid off two months later due to 'change in business direction'.

It's the flip side of 'at will' employment. Unless a company is willing to put it in contract, I would recommend often showing little hesitation in not being more open about your future plans than you need to be.

If a company demands/expects loyalty, can you say that you expect they'll show the same loyalty when it's not working out for them? In the vast majority of cases (and it's not even necessarily malicious), absolutely not. You'll turn up one day, have a meeting with your manager, and, if you're (very) lucky, get some form of severance.

Quid pro quo.