I get slightly different behaviour with a KDE desktop (started from gdm though). In my case I tried "init 1" and most processes, including the X server, were eventually killed. However, I had waaay too many processes left by the time I got to the single user prompt. As I recall, there were about half a dozen of which the only one I can remember is the
openoffice.org quick start thing. Obviousy the only things that should have been there are the single user shell and the kernel-context processes.
This looks like a problem with the upstart-init not actually killing off everything it should be killing off.
jch