I think the question is very valid and simple…
What is the intention with the PostMessage functionality, why is it there and what can we do with it?
I also miss other functionalities that are often present for webviews. Like can you notify me when the URL is changed? or even let me know what the URL is?
I know there is a getURL function, but it simply returns the URL I initially provided. If user navigate to another url, the same URL is returned from my webview, that is not nice.
Do not get me wrong, it is nice to have a webview, but we need more and we need examples 
Just my 5 cents…