> I'd knock a star off if delivery was delayed because it didn't ship on time though, which has happened on more than one occasion.

That's the point! You don't knock a star off a product because they didn't ship the product in time. You knock stars off the SELLER. There's literally a whole system in place to review the seller.

And if the seller is Amazon, it's even worse. Why would I care about whether or not Amazon was able to ship your product in time 3 months ago?