How often should top fighters fight top fighters?

[pacmanis1]

I ask because I'm looking at the ring's top 10 jr middle weight and you only have three fights with two top ten guys are fighting each other. You have Mayweather vs Cotto, Lara vs Molina, and Angulo vs Kirkland. Don't get me wrong, I'm not trying to **** on those fights but May/Cotto wasn't really about weight, and Molina/Lara only gained significance after the event. I'm a big fan of jr welter weight and there you have like six fights between top guys there. You look at super middle weight and you got like 6 or 7 too. So all in all if you look at a divisions top 10 how many fights between the guys should you be able to count?