I'm not sure what fervor means here, but in 2009 F1 events had a total attendance of about 2.8 million. Whereas NASCAR had a total attendance of about 3.8 million.
I can't find one either: but I'm not sure "I saw it on TV" is as good a measure of "fervor" as "I paid good money to attend it in person."
As to number of races, surely a moment's thought will convince you of the speciousness of that argument. That's like saying "Sure, The Dark Night had a bigger take than Moneyball, but it was on so many more screens."
Attendance wise, NASCAR is local. Its in one country and sort of moves locally. F1 drops down in countries, then disappears. The whole thing is different. Frankly, I think its pretty hard to properly compare the two in any reasonable way. Its pretty much like comparing hockey with basketball, there are similarities, but they are totally different sports.
BTW, I am one of those rare things, a British NASCAR follower. Not exactly a "fan" as such; I enjoy it, but I'm not knowledgeable beyond the obvious. That said, F1 is my main thing. One of the reasons NASCAR appeals to me is the almost complete contrast with F1 (and Indycar, which I also watch).
