I was with you until I saw the screenshots in the TC post. The first one with the same layout right down to the seal of authenticity below it - this is way more than using common industry recognized design elements (like Fab using Pinterest's grid layout for example). This is close to Samwer brothers territory here.
They're also not doing themselves any favors with their response to Fab. Raising a lot of money and having scale doesn't automatically make Fab a villain. The claim on using open source frameworks is just bizarre/irrelevant.
Most of all, this doesn't pass the sniff test for me. At a quick glance, I could have easily mistaken this site for something built out of Fab. If I were Fab, I feel I would be angry and want them to stop copying my work directly.
"There might be 10 clones here, [but] there are also 20 clones from the United States right? You know, being copied is something that I think that every successful company will go through. Our biggest defensible asset really is our community, and I think that’s the thing that you’re not going to find on any of these replicas." (http://techcrunch.com/2011/11/06/instagrams-kevin-systrom-on...)
and Instagram didn't sue their clones !!.
This insinuates Fab.com is suing because Touch of Modern has a similar business model.
However, I now sense this is deflecting the real truth, which is that more than just a business model and the use of Helvetica is being copied.
If I were Pad, I would at the very least get legal advice the minute I saw that.
It may be without the bounds of what is legal, but it is certainly unethical, and it pretty much voids anything the OP wrote about this. This isn't a brave little start-up, this is a bunch of cheap-ass copycats with zero originality.
A lot of HN commenters are having the opposite reaction, not just you, and so I suppose you all might be onto something. But I still don't see it myself.
Aside from the choice of layout of the product page, which itself is generic, I don't see anything in common. Having the time remaining in the header bar has been commonplace on flash sale sites (Groupon and clones) since before Fab was ever founded.
E-commerce layouts have been studied in depth, it wouldn't surprise me if the layout choices (like repeating the add to cart button at the top and bottom) by Fab were not arbitrary but based on known best-practices.