The 10% increase in CTR from having the badge in your ad is a big incentive to search marketers. Theoretically that should decrease your click costs 10% or allow your ad to display in a higher position for the same bid.

The 40% conversion rate increase seems dubious, unless it applies only to current G-Checkout users, which as other have said are few and and far between. Amazing with Google's clout and advertiser perks like this their market share is still pitiful.