Yeah, and Google knows exactly the same thing, probably in much more detail. That's why it returns mostly sales sites.
But, according to you, if Google throws in one informational result -- one -- for the few folks who aren't looking to buy and you see this as "a cornerstone in Google's strategy of keeping AdWords ctr rates on the increase"? I think that's a pretty long reach. Sound more like G is trying to satisfy the broadest possible user base.
Google has a little knob it can turn (not sure what color this one is), that adjusts the mix of types of sites returned for a query. If as you say the overwhelming majority of searches for "jewelry" are for buying, then it appears that G has this knob set just about right.