IMO, the vast majority of programmers wouldn't meet the definition you've put forward here. I don't know many that dig into the operating system, platform, or hardware all that much, though I work in streaming media so that might just be an industry bias.
That said, it's rarely pays out. Quite the opposite: I often spending lots of time digging unnecessarily. I'm not complaining, I am who I am and I don't want to change. Digging into internals makes me happier and satisfied. And sometimes it is useful. So Linux kernel internals are on the roadmap and hopefully I'll dig into it some day.
I agree that absolute majority of people I met are not of that kind. And probably they should not. Learning business side of the software is what makes someone really useful. I hate business side, I only love computer side.
I'm working in areas of systems programming where such knowledge and willingness to go deeper into the stack is helpful, even if rarely so.
I can't say I understand the kernel, I only scratch the surface of most of it and only dug deeper where I really needed to and only as deep as time allowed me and the need required though.