Panasonic apparently pixel binds 2x2 pixels to reduce the sensor's full resolution to 1/4 before reading the sensor (approximately 12Mp to 3Mp for the GH3), then further reduces that when processing to "FullHD" (about 2Mp).
- http://www.imaging-resource.com/news/2012/09/28/qa-with-panasonic-the-story-behind-the-new-gh3-and-compact-system-tech
Also Panasonic claimed disabling the multi-aspect feature of the sensor helps them improve their sensor reads, enabling 1080p60 as well as a cleaner image. This makes sense since the GH2 had to down res approximately 3.5Mp to 2Mp with an older processor while the G6 will be converting 3Mp to 2Mp with a newly developed processor designed to further increase signal to noise, preserve details in noise reductions and widen dynamic range. Checkout the G5 since it also used the GH2 sensor with supposedly better results, and it did it without this new processor. (I'm still trying to track down where I read all this so take it with a grain of salt)
Can't help to think this could be Panasonic trying to show off what they can do with their own hardware technology, vs the Sony sensor in the GH3, justing on the specs and price Panasonic seems to be ok "cannibalizing" some of the GH3 sales to make this point.