You can access the clipboard and alter it, copy it, paste it, but you can only paste what is in the clipboard via a paste event. This has to do with Security issues.
Flash Player requires that the getData() be called in a paste event handler. In AIR, this restriction only applies to content outside of the application security sandbox.
See http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/desktop/Clipboard.html#getData() for more explanation.