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1. Just because there is some huge number of results for a given search doesn't mean that there are a lot of people searching for the term (think of a search for 'the', which brings in a huge number of results, but no one searches for 'the').
2. In my experience some areas are dominated by Google searchers, even though a website may rank equally in Y, MSN, and G for the same terms. I believe different demographics use different search engines, and this may account for your issue.