Get-ScheduledTask is a feature of specific versions of Windows, not a version of PowerShell. Ergo, it doesn’t exist on some of your computers.
“WinRM quickconfig” isn’t the best way to enable Remoting. Enable-PSRemoting is the correct way to do so. However, simply enabling Remoting doesn’t make cmdlets available on computers – Remoting is just a communications protocol.
PowerShellPack.msi isn’t a Microsoft thing – I’m not familiar with it.
So, short answer to your question, you seem to have thrown a bunch of spaghetti at the wall, and only some of it stuck :). I think before you do anything else you might want to fall back and read up a bit on PowerShell, because you’re definitely overkilling it.
Have you considered just using WMI? It exists on every Windows computer. You can run Get-WmiObject to retrieve scheduled task information from remote computers. See http://msdn.microsoft.com/en-us/library/aa394399(v=vs.85).aspx for the Win32_ScheduledJob WMI class.