I think the 7800gt either doesn't have any more pipes/shaders, or they're hard disabled and can't be re-enabled. I tried to unlock my 7800gt with rivatuner, and it let me change the settings for the pipes and shaders, but even after rebooting the settings wouldn't "stick," it'd revert back to 20/7.
Mine shows that pixel unit 3 is "disabled" and that vertex unit 7 is disabled. By it saying disabled, then I assume that it has the units on the card. Nvidia may have done hardware modification to prevent them from being enabled, like what could be done for (some) 6200 and 6800 cards.