I can't help but think we're involved in something approaching sheer speculation. Just how Google differentiates between .com and co.uk (or, for that matter, .ca) is known only to them -- and I suspect they keep changing their rules in any case.
I can recall making a post to the effect that all at once I was showing up in the Top Ten in both Google and Google.ca. It wasn't a great many months back, but it didn't last too long and I'm now resigned to the way things were before.
I have a .com site with a Canadian host and I do well with the web searches but only occasionaly so in pages from Canada. To add to this confusion, my Google page is in fact labelled Google.ca, although (for reasons that escape me) it doesn't seem to make any difference if I use either my Google toolbar or actually go to Google.com to do a search.
All told, I don't think we can make any assumptions as to whether our domain extension or our host location -- let alone changing them -- has any effect. It seems to be entirely in the lap of the (Google) gods and they ain't saying nuthin'.
Duncan
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