This seems very, very plausible to me. Jobs in this experience level and pay range aren't generally posted publicly, and don't stay posted very long if they do go public. This reminds of the same sort of phenomenon with "the good houses"—they never make it to market because someone knows someone knows someone who wants a house like that, so they get first shot at it.

These sorts of jobs are best found through one's network. Not only does this open up better opportunities, but this sort of "back channel" opportunity usually comes with more details than a public job listing (such as the "I think they're probably paying $YYYk or so").

I think this is a major factor, but it has still happened to me even when interviewing for boutique jobs via a friend's reference or happening to know someone who already worked there.

A fair amount of the interviews I accept come from unsolicited head hunters seeking me out, and even then the reveal-your-salary thing is a huge sticking point. And even when it hasn't been, I've still been let down by the ultimate salary offers.

I heard once that you should budget 1 month of job searching for every $10,000 of compensation you seek, and maybe more once you are seeking high-level bonuses. That's easily been true in my case. You also have to put up with horrid HR people who are quite simply just rude to you, and lots of degrading "dance monkey dance" whiteboard and coding puzzles and hazing, and demoralizing cross country interview trips that you have to muster the ability to put your whole self into but which you cynically know in your heart of hearts that it's a waste of time.

A substantial proportion of jobs never even makes it onto job boards. And yes, higher paying jobs are often amongst them. I've been approached for jobs that have never been listed publicly several times. It's one of the reasons why it can pay to be on good terms with (the right type of) recruiters and (more importantly) have a good network of industry contacts.