There is a sensor near the top-left corner of the DROID that senses when the phone is next to your face. At that time, the screen goes dark. I am under the impression that the screen at that time is "disabled". You can experiment with this by placing your thumb over the screen near the top-left corner while a call is in progress.

 

there is a sensor on the phone that shuts off the screen when your face gets close... there are several threads regarding this issue already. check out the forums search feature!

 

I think you're correct. Since it's a capacitive screen, it needs to have power in order for the touch capability to function properly, so when it's "off" due to the proximity sensor, the touch should not work at all, by design.