Its true that powershell being a new tech probably doesn't have the large library of "known ways" to do things that the UNIX world has. And BTW I'm not even a powershell person. I write embedded software in C++ for a living ! Having said that, I'd imagine you would parameterize something like

  Invoke-Sqlcmd -Query "SELECT ..." and write it out to a file? 

or avoid it and just use BCP "select blah" queryout "c:\file.jpg" etc etc