It's the easiest way to display complex graphics on the Kindle which take over the entire screen. Yes, I could use HTML and the browser, but there's a header and footer that I don't want to see (plus I'm not convinced the Kindle would stay awake). I could have sent text, but the renderer available at the CLI is extremely limited. I'm not sure if I could have tapped into a mobi/pdf renderer to make it show up similarly to an e-book, but I'm doubtful if I could have made a mobi file show up in landscape like this. I was also building on several other tutorials that use PNG files, so it just made sense to do this.