I would disagree and say that while PowerShell is well...powerful, it's not as pluggable as the Unix shell. Purely due to objects vs plaintext. PowerShell works off of .NET objects thus if I want to take output from one command and send it to another I have to verify that the receiving command can in fact receive the object type I'm sending. This is where the Unix shell to me is more 'pluggable' but it makes it more muddy as well. I can pipe plain-text information to any utility but to ensure that it will do what I want and not error out I may have to slice and dice my initial output a bit.

Maybe to you pluggable means an output object from a utility being the same input object as another utility? In this case, Unix isn't pluggable at all.