I'm from the UK and over the last four months I see BING's share increasing by less than 1%.
But the eCPM, CTR and everything else for my sites shows that BING converts page impressions into money at roughly 2.5 times better than Google.
Why? Because their results are better than Google and therefore people click on the Adsense ads ads more. Or because the results are worse than Google and people find the ads more attractive to click on?