On the infiniti.com website there are many of the same items under accessories and individual options like the cargo net, cargo mat, rear deck spoiler, splash guards, illuminated kick plates.
It is significantly cheaper as an "accessory." Why is that? Is it because it doesn't include installation?

I can't speak for the spoiler and illuminated kickplates, but you can usually get them to throw in the cargo net and trunk mat free anyways...