Correct me if I'm wrong, but American Boxing PPVs did far more sales in '07 than UFC PPVs did. '07 was a huge year for boxing, heralded as a big comeback over the past couple which were, admittedly, lacklustre (UFC PPV sales outdid Boxing in '06, though not by much). UFC had a huge spike in popularity due to its coverage on, well, SpikeTV, with the reality show doing wonders for its mainstream appeal.
Mayweather IS a household name in a great many places, as much due to his boxing as his appearance on Dancing With the Stars (re: mainstream appeal).
As for Superfights -- they don't happen all too often, and it's really a term that's somewhat confusing anyway. In days past, a superfight was one that got the non-boxing-fan public to tune in... that doesn't happen anymore, because big fights have solely been done on PPV.
Ali-Frazier, Hagler-Hearns, Leonard-Hagler.... these fights weren't PPV (to my knowledge, anyway), and thus were huge cultural and television events.
Calzaghe-Hopkins is the first "superfight" for '08, and there are more. Some might argue that Klitschko-Ibragimov is a superfight, if only because it's to unify two of the heavyweight titles... but that's suspect.
[Edit: Apparently the Calzaghe-Hopkins bout is on HBO, not PPV... superfight indeed)
De La Hoya's next fight (a tune-up for the rematch with Mayweather) will be on free TV, not PPV, and he has hinted that Golden Boy Promotions may explore this idea further in the future. Maybe we'll see some true superfights in the not-too-distant future as boxing promoters realize the HUGE market that is free (and "reality") TV can make them as much and more money than PPV.
In short, if you think Boxing is dead / on the downspin / of zero relevance, you're just flat wrong.
On that note, I'm not really a wrestling fan anymore, though I follow the W periodically. I'll be watching this year's Wrestlemania, however, because Floyd will be there. I know I'm not the only one.
The fact he's being booked as a face still baffles me.