As a judge of the competition I was surprised when I heard this. I certainly wasn't aware of this while judging. Coincidently the judges were half Nikon shooters and half Canon!
As for the results, I think that Nikon's are still much more popular in UW shooting - most probably for historical reasons. That, and the fisheye. Also most of the people who were winners in this comp are well established UW shooters who have been shooting for years, and most are film converts. So they stuck with Nikon - as Canon had very little presence UW before digital.
Canon DSLRs are getting increasingly popular, but mainly with people who did not shoot an SLR UW on film. And generally these newer photographers are less likely to win big comps, but this will and is changing. I certainly think that an entire Nikon winners circle is highly unlikely to happen again.
I think here at WP we can get the impression that Canon is perhaps more popular UW than it is because the majority of the moderators shoot Canon, as do several other regular posters on the forums.
But I see the opposite at Magic filters, where we sell about 5 Nikon filters to one Canon. If that is any guide? Most housing manufacturers will tell a similar story - although perhaps less so with the brands that are bought most by newer converts.
Alex