Originality is overrated. Various sites with CSS-only layouts and minimal interfaces are best described as an emergent aesthetic. Expect more like this.
There are simply too many people drawing from the historical experiences and examples laid by e.g. Metafilter, Digg, image boards, etc. for it to consititute individual acts of copying. That there are so many whitelabel apps & plugins ready for the implementing only accelerates this evolution.
It's not convergent evolution when people are copying, but copying doesn't obviate emerging aesthetics. Once upon a time, websites did not all have menu bars across the top, is this a result of despicable copying, or of lots of people simply deciding it was a good idea? Whether or not I think a given UX trope is useful is irrelevant to others choosing so.
My assertion is quantity-neutral. I simply don't think it matters how much is copied, just the fact that any copying is going on at all signals that the look and functionality is having an influence.
They "design in code".
http://www.quora.com/Joel-Lewenstein/Life-Without-Photoshop