Missing "show package contents" cmd
Show Package Contents is not for showing the contents of .pkg files, it's for showing the hidden structure for Applications (and other bundles), which are actually folders. You can use the program Pacifist to look at the contents of .pkg files.
To answer the question in your comment, here's how you can tell in Terminal. When you perform an ls -l
command, directories have d as the first character in the line.
516 $ ls -l
drwxr-xr-x 3 steve admin 102 Jan 6 2011 Form Viewer.app
drwxrwxrwx@ 3 root admin 102 Jan 18 2010 FormViewerFonts.pkg
-rw-r--r--@ 1 steve staff 2157020198 Jun 30 2012 MacTeX-2012.pkg
In this example, the first two entries are bundles and the last isn't.