Not that I can tell. My guess is that 'deleting' a comment actually sets a 'deleted' flag somewhere in the data base rather than actually removing it; but I haven't looked at the code so I'm just speculating.
> Is the idea of negatively voting down a comment ... To encourage the user to delete it?
No. The purpose is to encourage commentary that follows the site's discussion guidelines:
Actually I was being facetious. :)
> Does deleting it remove the lost karma?
Not that I can tell. My guess is that 'deleting' a comment actually sets a 'deleted' flag somewhere in the data base rather than actually removing it; but I haven't looked at the code so I'm just speculating.
> Is the idea of negatively voting down a comment ... To encourage the user to delete it?
No. The purpose is to encourage commentary that follows the site's discussion guidelines:
http://ycombinator.com/newsguidelines.html (see section titled "In Comments")
In fact, the window to delete a comment is only open for a set amount of time after posting, after which the site withdraws the option to delete.