What are the benefits of not using an iframe to embed one site in another?

Question

I was studying how Disqus and other embedded wigets are implemented, and I came to realize that they don't use an enclosing iframe where all their widget is run. What they do is to append elements dynamically to the embedding page through JavaScipt and then run almost every form or button in some iframe. What's the point of doing this? Couldn't they just wrap everything in an iframe and then change the parent window URL (to allow navigation) through some kind of cross-domain messaging system such as easyXDM? Can anybody point out some benefits that arise from having some elements not inside an iframe?

Answer 1

1. Code inside an iframe may not be able to set cookies as browser thinks it is an advertisement.

2. Iframe content cannot control the size of the outside iframe, so iframe needs to be created with javascript and javascript needs to be loaded externally so that external site has total over iframe size.