1. you paid for things three years ago with GW/NFC. And Google knows exactly what those things are.
No sir. That's an oft-repeated myth.
Google has no way of knowing exactly what items we purchased, any more than the credit card companies do.
That's because the only related info that merchant POS terminals send up, is the merchant id and category, plus the total amount. They don't transmit a list of what was bought.
Apple has no info about AP transactions because those transactions are between you/merchant/EMV/bank. Apple is NOT an intermediary, as Google is in the GW scenario
According to a leaked Apple Pay contract, Apple requires the credit card companies to provide extensive, though anonymous, information on types of payments, purchase amounts, locations, etc. This is reportedly one of the stumbling blocks in getting Apple Pay accepted by UK banks.
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In either case, it's not Apple nor Google that we have to worry about. It's the banks themselves. They not only sell anonymized information about purchases to ad companies (one of the reasons they paid Apple to let the info continue to flow to them), but more importantly they watch our personal spending habits for patterns that might indicate a future inability to pay. E.g. buying at a liquor store or paying for counseling in the middle of a work day.
In such cases, a proxy merchant like Google Wallet which hides the real merchant category from the banks might be a very desirable privacy feature. (However, Google's made deals with more and more providers to let the real category through in order for the user to get specific extra rewards, so it's not a reliable category hider any more.)