Every other series in the world wishes they could be even close to having the success Nascar has... and continues to enjoy.
I had this very conversation with somebody on Saturday. Here's what I said: "NASCAR only wishes it were Formula 1." In terms of fans, global popularity, and money, NASCAR would like to achieve the NFL's status. They've got a long, LONG way to go before they are comparable to F1.
The on-track products are completely different.
If there is a series where there may be tighter control and more capricious interpretation of the rules, F1 is it. If I mock NASCAR for its controlling clutches, be assured I do the same for F1. Thankfully, F1 is going to reduce some of this, with engine homologation going away very soon.
Because there are fewer races, and no "chase", teams fight tooth and nail every race to qualify and finish near the top. Very seldom will any team ever try to have "a good finish" because one or DNF's can destroy a driver's and constructor's championship hopes. Also, teams receive massive cash rewards for scoring championship points. For the most part, the driving to win is nearly 100% of the time in F1 and I'm convinced that isn't the case in NASCAR. This is sensible given the way the series are structured.
The cars are as different as they appear. Driving both well is difficult, but driving an F1 car is just plain violent. They decelerate at 1g or more just by lifting off the throttle; applying the brakes raises that to 5g. They develop so much downforce that they could be driven upside down, and even turn right and left, were it possible to get them into that position.
There is no doubt that NASCAR dominates racing fans in the U.S.A. Get beyond those boundaries, though, and you'll see it for what it is: a successful regional series dwarfed by F1. I'm not criticizing NASCAR; they seem good at what they do. I'm disputing the notion that NASCAR is the most successful motorsports series in the world. It's not even close.
Disclaimer: I'm not a NASCAR fan. I don't like the racing -- especially ovals and "competition cautions" -- so I choose to watch very little. But there are two races per year that I love to watch: the two where they turn right. If they ran more road courses, I'd watch a lot more NASCAR.