The release of the England & Wales 1911 census has actually destroyed a lot of myths about how the census was taken.
Many people think that emumerators went from door to door filling in the books from questions asked, and they think this explains mis-transcriptions due to people being mis-heard.
The real truth is that every census has been held in the same way - census schedules left with householders to fill in; census forms collected; census data copied from the schedules into the enumerator's returns books. The questions asked have varied from census to census, but the way the census is held has never changed.
The only difference was that the householder schedules for the 1911 census were not destroyed, and have been made available for public view. This is the first time that people have been able to see their ancestors' handwriting on a census (even though sometimes it's not clear who filled the form in).
Getting back to the Ancestry 1911 debate, I think Ancestry are reluctant to spend a lot of money on giving the 1911 census to its subscribers, because many of them will have already accessed the information via Brightsolid, so it's not an urgency for them.