Yeah, it's a huge joke.
Tube chassis full-on race cars with gigantic V8s...with fibreglass bodies. They slap stickers on them and call them street cars, including the Toyota Camry for a while (a V6 economy front wheel drive economy car).
Now, they may have some microscopic 5% relation to the road car (maybe the wheel bases, or something?) but as a whole, not related at all in any way to street cars. Oddly, NASCAR began as a form of touring car racing based off booze-smugglers cars. It then became more touring-esque with cars based off of showroom muscle cars. Now it's absolutely nothing related to normal cars.
People are still die-hard Ford or Chevy fans...even though there isn't much to those claims now. They'd be better off watching Continental Sportscar Challenge where they actually raced Mustangs and Camaros against each other etc.
The popularity of NASCAR is not so much in the actual racing. It's popular in the South among country people because all of the engineering centers are based down there and the majority of drivers are from the South. The attraction to the events is far more 250,000 people getting together to get drunk for three days in their trailers - and occasionally a motorsport event breaks out.
There are a heapload of people who spend the entire season driving their motorhomes around, following the series, sometimes too drunk to actually watch the race. That being said there are some actual motorsports fans who follow it - but it's popularity is not due to the hardcore racing fans. It's more of a life-style thing.
When a NASCAR race shows up to a city in the South people stop working, shops shut down, the whole week is tailored to the race. It's ingrained very much in the culture down here. The atmosphere is tremendously different from an Indy Car race, or a Rolex Sportscar race. Not to say one is worse or better ---- but NASCAR is its own animal.