They already had made a strong statement by choosing BSD when GPL was at their disposal. That is a much stronger statement than some blog post that reflects a momentary snapshot of their plans.
It is just that people don't hear what they don't want to hear. Every BSD or MIT is a loud and clear statement to deny the guarantee that derivative works will remain free and open.
Because Redis said they would never do something and then changed their mind (which makes the whole concept of saying you will never do something useless), while Amazon never said they wouldn’t use open source software for free (which is their right).
