Oh good, I was hoping someone would side with Stu. Muhahahahaha....
Stu is barking up the wrong tree. Nikon has been doing optics for generations, and is an industry leader. R&D, marketing, cost of doing business...all that is factored into their pricing. But you know that already. Their stuff is expensive for a reason. Because it's worth every penny.
Enter Sigma. They're an aftermarket brand. Their business model is not to innovate, create, or lead. Their business model is to copy, shortcut, and cheapen. That's not necessarily a bad thing, and it happens across all business markets. There's always a knockoff brand out there that is similar and cheaper, but not a good.
Take our industry for example. Photographers...there are pros and amateurs. Pros have the equipment, knowledge, and experience to get the job done. Amateurs might have similar gear, but not nearly the knowledge or experience. Yet some buyers will go with the amateur simply because the pro comes with a premium price tag.
In this case, Nikon has tried unsuccessfully to resolve the matter out of court. I'm sure they realize that Sigma is often a gateway to their Nikon products. However, there is some protected technology here that has been infringed upon that helps Nikon maintain its elite status. They have every right to protect themselves.