No this has nothing to do with friendly payloads.
Also, you can't just send one action to another action so the fact that TTS selects randomly from "piped" phrases is not relevant.
{LastResult} is the result that was returned by the last action that returned a result (some actions do not return anything).
{LastSpoken} is the text that was last spoken by the user (actually it is what was recognized) , not what was last spoken by the TTS engine.
If you want to send chat text with Skype you need to add your own action for that to your macro, in addition to (or replacing) the TTS.Speak action.
The variables you are trying to use are all explained in the wiki:
http://voxcommando.com/mediawiki/index.php?title=Variables