I don't think the Eltham=Ham, Fulham=Ham, Ilkeston=Keston, etc. is an error made on the part of the transcribers. Since it is so widespread, it looks more like to me an error when Ancestry compiled the database. Assuming the original data is correct and still exists, I would think it may be an easy thing to fix.
The 1911 census is particularly difficult for transcribers because each household is in a different hand. At least on previous censuses, as you transcribe a town or village, you can get used to the way the letters are formed and see trends. Can't do that on the 1911!
Really the transcription errors are no more appalling than those found on FindMyPast for this census. I don't quite understand why people seem to expect Ancestry to invest more time and money into producing a better transcription than other commercial sites? Poor Ancestry really can't win, no matter what they do. Either people are complaining why certain records are not available yet, or complaining that they did the work too quickly.
Besides, if everything was transcribed perfectly the first time, that would take half the fun out of our searches...
