Linux is a black box for 99% of its users too, since having access to the source and being able to comprehend a small fragment of it are vastly different things.
Practically speaking, for sysadmins, whether source is available is not always (or often) going to be terribly relevant.
No, actually, that's a horrible analogy.
If we must analogize, Linux is deep water. Almost infinitely deep. So deep, in fact, that few choose to plumb it all the way down. But it remains visible and accessible to the level of every sysadmin or developer's needs. The fact that most people prefer to skim along the surface takes nothing away from the volume of information waiting to be explored.
And now, because I'm forced to indulge in silly analogies, I find myself compelled to say that Windows is a swimming pool. A large one, it's true, and a crowded one, too. But you cannot easily move beyond its (broad) confines, you have no insight into where the water comes and goes (a topic which increasingly preoccupies my thoughts as I consider the statistical likelihood of people pissing in the pool), and you have little control even over your own course as you are buffeted and blocked by the arbitrary actions of others.
Finally, to get things back on a more practical level, PowerShell may do wonderful things, but the thing that makes Bash so compelling is the environment it runs in. Bash itself is a bit awkward and limited, but it's just glue for binding together countless ingenious (and sometimes even elegant) commands and utilities that can allow you to do things in minutes you couldn't really contemplate doing on Windows in comparable time. In fact, the only way that Windows seems to be able to compete with *nix on the server side is by appropriating the very things that make *nix so compelling.