I have been doing some more homework on GH2 video and also been talking to Mr.Uematsu at Panasonic. The sensor outputs video footage progressively at all times, including 1080 at 50 and 60 fps. As we already know, 1080HD 24p AVCHD footage can be recorded and it used to be at 17mbps but is apparently increased to 24mbps after the firmware update.
Mr.Uematsu only says that 25p and 30p recordings are possible, technically, but files are encoded in 50i and 60i, respectively.
I wonder if this is something to do with the codec? AVCHD actually uses the same H.264 codec as the E-M5 but the packaging is different (AVCHD uses .MTS files and Olympus chose .MOV for its MPEG-4 AVC packaging). H.264 requires a lot of horse power for compression. Panasonic's Venus Engine was upgraded to 3 and then 4 cores to number crunch video compression adequately. Olympus TruePic VI was also upgraded to multi-core hardware last year.
I need to do some more research - but I'm beginning to understand video a little better