haven't Genes got it now?
FindMyPast and GenesReunited are both owned by the same company, Brightsolid, whilst GR does seem to have a different index to FindMyPast its likely they are accessing FindMyPast's images.
One of the reasons Ancestry (and others) don't have it yet could be cost. Both FindMyPast & GR have subscriptions with or without the 1911 census (FindMyPast also has the 1911 census as a stand alone subscription) but in all cases you are paying about 40 GBP for 6 months subscription to the 1911 census componant. At this stage Ancestry (and others) may well feel that the purchase price plus cost of transcribing cannot be absorbed.
I seem to recall that one subscription (not Ancestry) site contacted its subscribers for their views and the figure of 3 million pounds was mentioned,
Andy