What are the reasons of allowing or not allowing Static Content to be served using a HTTP POST?

What are the reasons of allowing or not allowing Static Content to be
served using a HTTP POST?

Some sites allow the images to be accessed via a HTTP POST request some
don't. What are the advantages/ disadvantages of doing either?
Sites which allow getting the content via HTTP Post :
Flickr
Facebook
(http://invalidlogic.com/2011/04/12/serving-static-content-via-post-from-nginx/)
Sites which do not
Amazon
Tumblr
Netlfix
What are some practical reasons for doing one or the other?