That's what I was referring to. Try buying a Kindle book — you have to wishlist it (you can't even add it to your cart) and switch to a browser to actually buy it.

This is also why I mention Amazon a lot: while I favor ApplePay for purchases, there's a 0% chance that I want to use it for my Kindle purchases because simply owning a Kindle means I've already committed to use Amazon to buy content for it.