The answer simply is "Cool-factor"...and size, and cost, and coolness.
It's an elegantly built computer. No, it's not as expandable as a desktop model, but with its USB connector, and a supporting OS, it is VERY expandable. It's more like a Laptop for youre Desktop. To me, the cool thing is not so much as its specs, but the creative things people have done with them. From using them as a full-blown computer to mounting them in their cars, from using them as Internet browsers to MP3 players, from use in an office environment to use in the kitchen, these puppies are flexible.
Oh, did I mention it's cool!