Yep, you're absolutely right, but he was asking if the 2010 FLHX pipes would fit on the 2010 SESG. Which they will, because they are the same pipe. Now if he was asking to put a non-cat version of the 09 FLHX on to a 2010 SESG, then you would have the O2 sensor issue and the flange.

Copied this from another post I made. Not sure if this helps but you can make '09 headers work on our '10 SESG's....
I have a 2010 SESG. '09 exhaust assembly (part # 66848-09) was used with "Adapters O2 Sensor 2010 FL" (part # 1861-0594). Dealer re-routed wiring since O2 sensors are in different location on the '09 exhaust. Also installed a SERT and V&H Hi-Outputs. Dyno'd at 97 HP and 113+ max torque. Runs strong, looks and sounds great - at least to me and others who have seen/heard it. Also mellows out at cruise so stereo w/Hog Tunes comes through loud and clear.