Yeah, but they aren't the only people that wear masks, in Kinnikuman. Actually, quite a few of the characters make a big deal about not revealing their face, which leads me onto this point.
Robin Mask and Warsman got their masks knocked off by Neptuneman and Big the Budo, during the Tournament Mountain. When it happened, the paparazzi went nuts, and the two of them were deathly afraid to show their true faces, for some reason. Probably not the same method as Kinniku Family, I'd wager, but still, there's gotta' be a reason.
Warsman, is obviously just wires and a huge singular eyeball. He lost his mask during a fight with Kinnikuman, anyway, much earlier on. I believe.
Robin Mask had like, uh, light brown hair, blue eyes, and looked like a handsome Disney Prince, or something. All the women in the crowd starting blushing, and for good reason!
Warsman without mask.
Robin without mask.
Wow, Robin does look like a Disney prince. xD And as for why Warsman and Robin being afraid to show thier faces, I'm pretty sure Warsman is ashamed of his inhuman looks (if I remember right, he showed Suguru his face in the darkness so only he could really see). .
In the episode were Warsman battles the Manriki, you can see flashbacks from Warsmans past were people humiliate him for his inhuman face.