Of course, the two shells may be equivalent in terms of power or number of features, and any contest a la "Can your shell do this?" would be futile. To me, it's a matter of cultural differences. Think of it this way: a shell operates in two mode, script or interactive (the new fancy word now is REPL). How much time does your average PowerShell user spend in REPL mode?
In comparison, a Unix hacker spends all his time in the shell, even for doing the most trivial tasks. As you practice more and more, the shell becomes a favorite way to operate a computer. Even tasks that may seem easier on a point-and-click interface (like selecting a few files from one directory and copying them into a new one) come more natural to me on the command line than with a mouse. The day I discovered that you can run 'for' loops from your interactive shell as naturally as a script, I almost uninstalled X :)
My only point is that the shell fits in the overall philosophy. You probably heard of the famous McIlroy vs Knuth story (legend?), where a pipe of a few commands turned out to be more efficient than a Knuth data structure. That's beyond my point. What I want to show is more the ending paragraph of this story, what McIlroy had to say about it:
> Very few people can obtain the virtuoso services of Knuth (or afford the equivalent person-weeks of lesser personnel) to attack nonce problems such as Bentley’s from the ground up. But old UNIX hands know instinctively how to solve this one in a jiffy.
That last sentence. Unix hands know how to solve these problems because of all the time spent on their command line.
Overall I'm glad that Microsoft is developing PowerShell, and I absolutely agree that it is far more adapted to their Windows platform than the old "all-is-text" mentality of bash and the POSIX tools. However, PowerShell is still treated as a second class citizen in the Windows eco-system, and that is, imho, its biggest weakness.