I, too, have not seen any evidence that either brand is notably better. There was a time, in the film days, when Nikon's lenses were clearly better, while the film SLR bodies were essentially equal. Over time, Canon's lens quality caught up. With DSLRs, Canon got a jump on the field and enjoyed it for some time. These days, all evidence suggests that Nikon has caught up to Canon in the camera field. The end result is that we have two companies producing essentially equal equipment in essentially the same price ranges. Then it becomes a matter of brand preference, which is purely subjective. I would argue that, after Canon and Nikon, there is a huge step down to the other camera makers.
I agree that there are a lot more Canon sports shooters in the world, but I think that's more a function of the lead Canon once had in DSLR quality and digital was such a natural transition for sports photographers because of the time/cost element in terms of getting images from camera to print. Wedding/portrait photographers, in the past predominently Nikon users, were not among the early adapters of digital technology. By the time digital quality caught up to film Nikon was starting to make progress with DSLR technology so it was likely easier to stick with the favorite brand.
The Nikon/Canon discussion will never reach a conclusion. Maybe I'll start a separate thread and we can have the same discussion about Macs and PCs. ;)
Gary