The 22 MP enabled 3x3 pixel binning as the downscaling algorithm. The fact the 1DX has 18MP and can't do that may be much to its benefit.
Pixel binning is just one step less idiotic a way to downscale than the line skipping the 5d2 did. But it is still so lame, and so unnecessary in 2012, that if any photo viewing app on a computer or even cell phone did it that way you would wretch at the quality of your photos when they were displayed at anything smaller than 100%.
The 1DX, to beat the quality of the video resolution on the 5D3, would use a superior downscaling algorithm. While I'm nearly certain the Digic5 could downscale video in realtime just fine on the 5D3, and Canon has intentionally dumbed it down to pixel binning in order to protect the C300, the 1DX has two Digic5's and Canon might have figured they could get away with claiming two were needed for better downscaling.
The better downscaling is taking away the residual stair-stepping (i.e. aliasing) on the venetian blinds that the 5D3 shows. However, the resolution is ultimately not that great...it may be say 850 lines rather than 800 that the 5D3 gets. To get over 1000 lines, you have to pay them over $15,000 for a "C" cine camera. But that is by corporate dictat and not by technical necessity.
The only bright side to this is the video on the whole DSLR line can be intercut with each other OK. The cameras over $3000 will have progressively less moire and aliasing, but won't have much more real resolution. The C series will be an entirely different level, and going across that divide (e.g. using a C300 A-cam and 5D3 B-cam) will require nimble work in post.