This also has to do with the audience. Just because an A/B test measured results on a listing of tea products doesn't mean much. Consider how Amazon displays their product: http://i.mking.me/3t3e2E3z2G1Y1X0T2633 I can imagine Amazon has ton a bit of A/B testing...
Audience, and also variance of product. The product images shown in the test are extremely similar, reducing the effectiveness of any arrangement that emphasizes visuals over details.
Amazon grids don't always use images that are quite as effective at indicating discrete products as the book-cover screenshot you've linked (just try browsing through headphones), but for a surprisingly sizable portion of their catalogue image-oriented browsing is both effective and enjoyable.
People like looking at pictures - but showing effectively the same picture over and over again for different products makes me (as a user) feel like I'm wasting time at best, mislead at worst ("the items in this list of unique things can't possibly all look the same in person, can they?")
