The NSX concept video was just that, a video for the NSX, that was rendered using the GT engine. I don't think it was trying to say it will be DLC necessarily.
The other video you are talking about is the same one that showed Seattle and Willow springs amongst other things. Admittedly, that was implied to be potential DLC, but with GT6 so close, I would suggest it will either ship with that game, or be DLC for that game later on after release. Or perhaps it was just dropped content that they decided against. Nothing was confirmed with all of that video content.
