I can already embed URLs in WordPress posts with a magical technology called "hyperlinks."
That's a "link" not embedded content. It's the difference between linking to youtube page and actually having the video in your post.
This provides one of the biggest reasons I was considering using posterous, although I did 0 research to see if WordPress already had a plugin like this.
How is this differentiated from any of the myriad plugins that already do this same sort of thing?