Maybe you are right and the 5DmkIII and it will be 22MP, but that would make a very strange line up for Canon. What will be the differences between the new 5D and the 1DX? This would likely mean there would still be a soemthing like a 1DXs in the work with a high res sensor, but then canon have already said that the 1ds and 1d lines have merged.
What would be the differences between a 22MP sensor and the 18MP in the DX, certainly not enough resolution difference to be noticeable.
Potentially the same difference between a 7D and a 1D Mk4 - the 7D is just less of the latter in almost every sense, bar resolution.
5D mk3 may well be a 'cut-down' version of the 1Dx - there is no precedent for it not to be (5D mk2 vs. !Ds mk3 rings a bell).
However, don't presume Canon to go all 'logical' to us mere public: the 60D is more like the xxxD line when it probably COULD have been a baby full-frame effort, introducing a new range of punter to Canon's more expensive EF glass.
Personally, I'd be mildly surprised if Canon didn't go uber-resolution with the 5D mk3, but hey... who'd have thought Nikon was go that way with the D800?