It doesn't rule it out unless we know that an open speaker jack switch means that there is no plug inserted. It is possible that this switch is closed with no plug inserted and opens when a plug is inserted. If this is the case, removing the speaker port makes the Mac think a plug is constantly inserted.

To test, you could use a continuity tester on your CC board on the audio out port's pins to see which pair open & close when you insert/remove a plug. It would be most conclusive to use some sort of non-conductive object that can be inserted, enough to physically activate the switch, either that or a stereo plug that is not connected to anything. I wish I had some old Macs handy, I'd test it for you! But alas, they are far away.