Earlier quoted context omitted.
The "big guys" sell a lot more products in a lot more categories, so are presumably putting in a much larer number of bids - it is not hard to believe that Google sees a lot more revenue from Amazon than some random knife shop.
I'm entirely sure that Amazon spends more. But for that keyword whoever bids the most spends the most. Google optimizes by the keyword, which of course they should, just as companies like Amazon don't bid on keywords because they're benevolent, but because they want to optimize their own return. Removing players from the market cannot possibly serve Google's financial interest, and that conspiratorial angle makes abs…
I don't see a conspiracy here, either - it just looks like the huge advertisers like Amazon have a lot more leverage in their relationship with Google than the tiny ones do, so are less likely to have the rules enforced as strictly against them.