I think its debatable just how much of a CCS the top valve is.
As it stands its a cathode follower. Leaving the extra AC gain from the cap, its action is to work as a cathode follower, and provide a less than unity gain low impedance buffer driven by the lower valve. So the lower valve provides gain, and the upper valve takes that gain and generates a low impedance version of the signal.
And the cap means that more of the anode signal is injected into the top valve, so if anything causes it to act less like a CCS.
Just my take on it of course.
Well, and stuff I read on pages like this http://www7.taosnet.com/f10/mustage.html
