They are doing something right. That's plain as day given recent results, as the growth is more substantial and consistent now than it was during the first half of the season.
Personally, I wish this had occurred last year, as I found the racing to be excellent. This style of racing is not for me. The playoffs aren't for me. I echo the sentiments above that I find NBC's booth and infomercial style presentation to be cringeworthy and godawful.
Nevertheless, when analyzing TV ratings and other business aspects of the sport, I prefer to deal in reality rather than what I wish were true. They have a lot going for them. They've made some shrewd marketing changes, finally. The Cup Series now seems to be out of the shadow of "Dale Jr. is gone" and "Jeff Gordon is gone" and so on. Finally, apparently the sort of fringe / casual viewers that make up the difference between 2.8 million and 3.2 million are enjoying this style of racing.
That's just that. I'm honestly more torn about the fact that NBC is experiencing all of this growth with their hideous announcing style than I am about the momentum racing doing well.