I agree with most here. Obviously the reviewers are incentivized to give good reviews so they continue to receive products early. With that said, Apple does make damn good products, so it is pretty easy to give solid reviews. Specifically when you are only spending a week at most with these products.
The Verge did a good job pointing out pros and cons. Most of the reviews I watched seemed like people who only spent "hours" with the device vs really putting it through its paces.
Bottom line. Do reviewers continue to receive products because they give favorable reviews, Yes. Does Apple make great products so it's easy to give a favorable review, Yes. Both things can be true.