Actually, I think it is YOU who are missing the point. Because if an Arduino will satisfy your needs, then by god, use the Arduino! If your project's small enough that a $30 Arduino UNO will be ample for what you want it to do, you'd be downright silly to build your project around one of these, instead.
But you're falling into the same trap that a lot of other people are -- thinking that all embedded systems have the same needs. Not all embedded systems need to be low-power, battery operated, or have no need for a display or a disk controller. Some robots need a lot more processing power than you can cram in an 8-bit micro, especially if you're dabbling in machine vision and autonomous systems. A document scanner (not to be confused with a document camera), laser printer, blu-ray player, and an XBOX 360 are all examples of "embedded systems", too.
The above list showcases another misconception about embedded systems: Not all embedded systems can stand alone. Sure, you could probably build a scanner around an Arduino -- I've certainly had scanners in the last 30 years that were built around much less capable microcontrollers -- but you'd need an external computer to drive the thing and to stitch the images coming off the sensor together into one single page and save that as whatever document format you want. If you just want to connect it to your desktop computer or you've already got a spare PC that you want to dedicate to controlling your project, that's fine. But you can save a lot of space and power if everything were able to be integrated into a single system.
I'm not trying to say that you should go out and buy a stack of these and use 'em everywhere you'd use an Arduino. That wouldn't make any sense. It's entirely possible that you, personally, are never going to contemplate a project that would ever need more than an Arduino UNO, or maybe you'll eventually upgrade to a DUE. And that's okay. Really, it is. But just because YOU don't have a need for something like this, doesn't change the fact that some of the rest of us might.