Invoke Keyboard Shortcut

A program like Keyboard Maestro can do exactly as you said, but instead of saving the AppleScript as just regular text you can save it as a script (.scpt) and just pass the path to osascript.

A program that I've used off and on that is designed to do this specifically is Red Sweater Software's FastScripts. It's free for up to 10 keyboard shortcuts. Otherwise I've just used LaunchBar (while others would recommend other app launchers)

I get the impression that what you're trying to do is a copy command (i.e., ⌘C)—am I right?

Here's an example from one of my scripts:

tell application "System Events"
    tell application "Microsoft Entourage" to activate
    tell menu "Edit" of menu bar item "Edit" of menu bar 1 of process "Microsoft Entourage"
        click menu item "Select All"
        click menu item "Copy"
    end tell
    key code 123
end tell

That is, I script the menu command instead of scripting shortcuts.

You might also take a look and see if you have /Library/Scripts/UI Element Scripts/Key Down-Up.applescript, which should give you alternate ideas of how to emulate keyboard actions.

And of course, there are a lot of examples in /Library/Scripts/ and ~/Library/Scripts/, many of which are worth a look in general.