[bradleyland]

It's a shame someone down-voted you. I'm not sure if you were being rhetorical, but this question is easily answered because the answer is, quite simply, "just about anything".

Want to add anything new to the page? Well, at Amazon-scale, your little widget is going to have to go through some pretty intense design review and load testing, because at over 150 million page views per day, tiny time penalties can add up to significant capacity issues.

Amazon is also notorious for deep introspection of user behavior, so any little thing you want to add is going to have to go in to the big bin of factors that might influence a customer to "click the button" (or not). Data about your new feature will have to be integrated in to the models that are used to evaluate user behavior, or at a minimum, the group who handles that will have to sign off on not tracking the impact of your new feature on user behavior.

The whole concept of "the group that manages that" isn't unique to Amazon, but once you pass a certain size, you don't simply add features or new products without a involving lots of people. That is a challenge unique to Amazon-sized companies.