Just finished transferring a couple of kits...one from primary to secondary, the other from secondary for a new carboy for stabilizing/fining/degassing. Incidentally, their sensitivity to oak-chip clogging and the need for 3-handed operation convinces me that auto-siphons are the tools of Satan intended to corrupt the holy process of winemaking. But that's another story.
After stirring in all of the stabilizers and finings agents, I whipped the wine for a while to get rid of the bulk of the CO2, put the oak spiral from secondary back in (I love oak), and then put it on the Mityvac to finish it off. As I sat there pumping, I got to thinking: If we're pulling all of the CO2 out of solution into the headspace, isn't it redundant to top off the wine? Any oxygen that got into the headspace during the transfer and stirring would surely be driven out by the flood of CO2 released during degassing.
Am I missing something, or is reducing headspace really only necessary once the wine is still?