What makes you say that, out of curiosity? I feel like Stitch Fix is targeting a whole other subset of fashion needs, and I've personally been really impressed with their operation.
Didn't get your point regarding whole sellers. As far as I understand this industry, the retailers generally source directly from brands and so does Stitchfix.
"their market position is dependent on their ability to match clothes for people"
That's their core competency though. That's what makes them successful.
That means that if you stay in touch with the newest developments it's actually pretty easy to still be sufficiently ahead of the masses to justify a service like this.
And if that sounds remarkably similar to how tech works: I agree with you.