The real question is this: does the dollar of earnings Amazon retains generate more than a dollar of value for owners of the company (i.e. shareholders)?
I don't know either way, and I don't want this post to seem like a criticism of Amazon. I know some people who work in upper level management there and they all speak very highly of the way the company is run (very meritocratic). But reinvesting earnings is only a good strategy if those earnings are put to good use, otherwise they should be paid out as a dividend.
Anyways, just something to think about whenever the topic of Amazon's profits/earnings comes up.