Let the hive mind of Engadget get that for you.
"I own an iPhone 3G and I'm looking for a decent speaker / alarm clock for it. I am going to listen music in a mid-sized room, so I want nice quality speakers with solid bass. I also want to use it as an alarm clock, so it would be great if there is such a feature. The price can be low-mid to mid-high range. I was looking at the Klipsch iGroove SXT; it's powerful, slick and the reviews are good, but it doesn't have an alarm clock feature. It's no deal breaker if I can set it up from the iPhone, but I'm not sure. Thanks!"
Yes, you can build your own; but that is only one small part of the market. What about all the others who don't even own a screwdriver, or want a turn key solution?
Also, less expensive NAS devices don't have the thruput capability to support multiple players, as this one apparently does.
One thing that Infrant does well is provide excellent network file and streaming performance due to the dedicated I/O processor.
The one thing missing is video or DVR capability.
Disclaimer: I am not affiliated with Infrant or Slim.