Loop is right if you look at the stats, but I think WSBK can be looked at independently from MotoGP, where the intensity of the competition is white hot and where all the very best riders end up, Biaggi and Melandri included. The two Italians got their one-way tickets to WSBK due to personality clashes on the one hand and woefully bad rider management on the other.
It is hard for the mortals amongst us to understand the differences when riding these machines at the top level, but riding a prototype MotoGP bike is definitely a black art that is best developed in the junior 'pure' racing classes, which is why superbike racers struggle. Cal Crutchlow is worth listening to on the subject, because he will tell you that he is still struggling to adapt from superbikes after his rookie season, even though he is going faster in testing than his traditionally-schooled teammate, Andrea Dovisioso. The business and politics of MotoGP are particularly brutal too, which makes it difficult for outsiders to come in on a truly competitive bike. And let's face it: there are only two competitive bikes in MotoGP and one of them, Yamaha, is stuck playing catch-up with the Big H. Remember Foggy's sorry experience in 500s?
WSBK is a more varied class today than it was in Foggy's day, with more nationalities challenging the traditional Brit-Aussie/NZ dominance which held back its international appeal. Adding circuits in more countries will help too. With a bit of encouragement, my Twitter followers tuned in and loved the racing spectacle from Phillip Island and are now asking lots of questions about the regs and riders.
MotoGP will remain unchallenged at the pinnacle of the support, but is in a difficult transitional period now, as Dorna tries to bring costs down and level the playing field. WSBK is grabbing the opportunity to take its show to a wider audience while the premier class figures out how to bring back exciting racing and who can blame them?