Thinking about staying fresh is great, of course you should do that.
Your hypothetical is fine, any sane person should do that. The problem with the engineer in question was that he clearly wanted to use the company as a stepping stone. While companies are fully aware that people move on, they are going to prioritize the people that seem like they are going to stick around for a while.
Turn it around and imagine you are the hiring manager. If your prospect is making it clear that the only reason they are hiring on is so they can go elsewhere, how does that make you feel? Remember, it costs money and time to bring someone in.
There is a difference between an employee and a contractor. A lot of what people are saying here would make sense for a contractor. A contractor is supposed to have a well honed skill set where they can come in, make a useful contribution right away, and move on to the next task. Employees, at least in my mind, aren't like that. The company is signing up to educate the new hire, that's an investment. In the places I've worked (system places like Sun), it was fairly normal that it would be at least a year before the new hire did any work that shipped. Maybe it's different now but that's the world I'm used to. So I'm looking at about $200K investment before I see anything at all hit the bottom line. In that context, yes, I'm looking for someone to stick around for a while.
Again, I'm old, but I've been hiring in the valley for 20, maybe 25, years. Maybe it's different now, but one screening technique everyone used was to look at how long someone stayed in one place. Someone who moves every 5 years is fine, someone who never makes it to 1.5 years is not great.
In this day of apps, maybe the dev cycle there is a lot shorter and so in that arena maybe you can pull in those numbers.