The default for a name or keyword search is "all boards", which searches all topics, surnames and locations - unless you select a certain board. Perhaps the message you are looking for has been deleted.
The boards were lasted indexed around 15 Nov 2012. A Google search often works better.
As far as I know, the message boards are the same whether you are on Ancestry.ca .com .uk .au. I'm not certain about the non-English sites.