Maybe Mint should scrape Amazon and other retailers in addition to bank websites? Would you trust Mint to keep your Amazon password in addition to your bank's? (Maybe Mint should pivot slightly to include password database management? :p )
Right now, our system is pretty much how you describe it, where the financial institution only gets the basic information of who and how much. And if you want more detail, the retailer provides it.
So I guess you're looking for a service that centralizes that info into the same place as your other financial details?
(paragraphs, please)