As a perl-writing Linux admin, I had to write powershell a couple years ago to do what would've been fairly easy with perl (progmatically, at least): a dozen or so nested logic structures, conditions, and what have you, based on the textual descriptors of various Sharepoint elements/objects, the end goal being to migrate multiple different Sharepoint environments into a single organized hierarchy.
This didn't work well. Neither perl-like text based sorting or the like worked well (because EVERYTHING is an object) or conventional OO type thinking. Quirky is an understatement. As for excruciatingly slow? Also an understatement: simple textual list sorts took FOREVER. And if that wasn't bad enough, sorting through a handful of 1-5MB XML files at a time (yes, using the proper XML functions) ballooned memory use to gigabytes. I ultimately resorted to dropping things to XML, doing the real work in perl, and then feeding the result back into Powershell - it was quicker, and the system didn't OOM in the process.
It isn't Powershell that's neat; it's Microsoft's integration of PS into its core OS functionality (and every other product) to allow for management and manipulation. That on its own isn't enough to justify using Powershell, unfortunately. It's just too damn unwieldy: it's like the undead afterbirth of COBOL, Java, Perl, and VB - leveraging only the unwieldy parts of each.
Thankfully, you're right: there isn't a burdensome, poorly conceived and implemented by Indians, management scripting language for Linux. But for everything else? We've got purpose built tools which do their one job, and do it well. (perl + puppet/chef, on the other hand, seems like a fairly close comparison to WMI...)