After adding an OS installer with PowerShell, you cannot distribute the GUI option 'Distribute Content' is greyed out:
New-CMOperatingSystemInstaller -Name W8 -Path "\\cm01\e$\Source\OS\W8"
The issue occurs with ConfigMgr 2012 SP1 and ConfigMgr R2.
The underlying server OS doesn't matter either (tested with Windows 2008 R2 and Windows 2012 R2).
The OS installer doesn't seem to matter either (tested with W7SP1, W8 and W8.1).
If I add the OS installer through the GUI, then the 'Distribute Content' button is available.