For some people, function is more important than function. They're great shoes, and considering where they're typically worn, does aesthetic appeal matter?
The ugliness actually appeals to some people, too.
This is an interesting point. It brings out the question: just how far can you make something ugly (assuming I'm not dead wrong about lack of aesthetic appeal in those slippers), provided that they do their non-aesthetic job right?
Certain famous websites come to mind. On a tangential point, it seems like these things must be relatively cheap and easily accessible, and cannot become status symbols. Sushi is an example where aesthetic appeal is as important as its palatability. (I'm typing a bit aimlessly)
So, what about those NIKE Naked shoes (or whatever?)? They are less of a fashion statement because they stand out less, I presume?
The only reason why they're a fashion statement is because they were born into a fashion-aware community. Check out my comment about the Boulder Country Club above.
Other than that, yes they are extremely light and comfortable...
The ugliness actually appeals to some people, too.