Well, how do you know they didn't purchase a demo unit from Razer either. Also, they may be known to enthusiasts, but they likely lack the broad appeal that a Newegg house brand would bring. Before you accuse me of being a Newegg shill, I'm just trying to play devil's advocate here and think of things in the most rational economic terms possible.
As for ripping off a design, I would argue that's a dicier topic, most of the time. That mouse does have a pretty distinctive design so it's much more blatant in this case. However, for it to be wrong, I think you'd have to claim that it existing is somehow damaging to the original designers, either directly in terms of sales or in terms of their perceived value. And maybe you could, but I don't have any numbers in front of me. Again, just playing devil's advocate because economics is interesting!