Data extraction and search engines

Such is the apparent dominance of Ancestry.com that I'm often asked whether I use Ancestry in my own family research.
Just to be a pedant, I generally use ancestry.com.au and ancestry.co.uk but now ancestry.com as I don't have any direct ancestors who went to America. So Ancestry hereafter.
The answer is yes, I do use Ancestry, probably in conjunction with Familysearch.org  but not exclusively as this little case study illustrates.
William Newman, a plaisterer, arrived in the colonies unheralded (jargon for I can't find him on any passenger list) to marry in Melbourne in 1852.
That means he was possibly captured in the England 1841 and 1842 Censuses and in London as he said that he was born in London.
But I've never been able to find him in either Census using Ancestry. Today I found that he is there all the time.
It was a gentle reminder to try other websites. Fortunately I found him in FindMyPast (http://www.findmypast.com.au/), the very first of six other websites I was prepared to try.
Why the success with one site and failure with another? There could have been a few reasons:

• the original census data may have been filmed more than once yielding different results,
• the data may have been indexed more than once with differing results,
• different pay to view subscriptions may have meant that different data was available or
• what I think was the case with William Newman, results may be presented differently. For example, a couple of small tests showed that although I thought my search parameters were sufficiently directed to a search in London I got lots of rubbish presented before the really critical information and I had given up before scrolling down the reuslts that far. By the way, I still haven't been able to put the basic research parameters into to get my required result. I used some of the source data which I had found on FindMyPast as keywords to show that the record for William Newman is indeed on Ancestry.

We had an excellent lecture from Phil Dunn, an English researcher, on using FamilySearch. The best bit was that wildcards can be used at the beginning of a text string. His lecture also reminded me that putting an ancestor into their social context may help to find them or answer the question "why did they do what they did." His talk also highlighted that the United States has been around a little longer than Australia!