If you have a theory about what Apple's motivation to actively serve such bad results could be, I'd be interested to hear it. I've always sort of assumed that the root cause for this is some combination of neglect on Apple's part and attempts at gaming the system by developers (I don't know much about developing for the App Store, but I presume there are forms of SEO-like activities that can be done in attempts to bump up your app).
I think it's reasonable to expect better from them.
Why promote an app with 100 sales over another with 10,000?