Which abilities are they not allowed to use?
Manlets have a marked advantage in grappling/submission in the UFC due to the banning of things such as groin shots, biting, knees/elbows, etc. They wouldn't be able to submit lanklets as easily if the entire arsenal of close-ranged attacks weren't 'against the rules', thus why submission moves have been so dominant in the UFC. Rulesets do have a place in sports, boxing being an example - the rules keep it as a pure test of sportsmanship: stamina, strength, cunning. That's not to say boxing couldn't do with some improvements in the rules department (see: Floyd "Gorilla Arms" Mayweather).