It's more direct than that, screen shots from the suit: http://techcrunch.com/2012/08/15/fab-lawsuit-touch-of-modern... (iPad app popup warning)
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.